Handout Struktur Atom Finall

7/31/2019 Handout Struktur Atom Finall

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Who Proposed the First Atomic Theory?You may know what atoms are: they are the tiny particles that make up all matter. Today,

we know a great deal about the structure and behavior of atoms. However, scientists have not

always known about atoms.

ORIGINS OF ATOMIC THEORY

The things we know about atoms today were discovered by many scientists over a long

period of time.In fact, the first person to hypothesize that atoms exist was Democritus. Democritus

was a Greek philosopher who lived in the fourth century BCE. He suggested that everything in the

universe was made of tiny, indivisible units. He called these units atoms. The word atom comes

from the Greek word atomos.Atomos means unable tobe cut or divided.

Democritus made many observations of how matter changes. He thought that the

movements of atoms caused the changes he observed. However, Democritus did not have any

evidence to show that his theory was correct. Although some people agreed with Democrituss

theory, others thought that different theories were correct. As the science of chemistry was

developing in the 1700s, scientists began to focus on making careful measurements in

experiments. Therefore, scientists began to collect more accurate and precise data about matter.

Just as scientists do today, scientists in the past used data to decide which theories were most

correct.

How Did Dalton Contribute to Atomic Theory?In 1808, an English schoolteacher named John Dalton proposed a different atomic theory. LikeDemocritus, Dalton proposed that atoms could not be divided into smaller parts. However, unlike

Democritus, Dalton performed scientific experiments to find data to support his theory. Daltons

experiments showed that atoms of different elements could combine in certain ways to form

compounds. This is known as the law of definiteproportions. The law of definite proportions

states that a chemical compound always contains the same proportion of a particular element. For

example, in any sample of water, hydrogen will make up 11% of the mass of the sample. In other

words, in 100 g of water, there will be 11 g of hydrogen and 89 g of oxygen.

DEVELOPMENT OF ATOMIC THEORY


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Some parts of Daltons atomic theory are still acceptedby scientists today. In fact, Daltons

explanation of how atoms combine to form substances is considered the foundation of modern

atomic theory. However, as scientists continued to carry out experiments, they made new

observations that did not fit Daltons theory. New theories were developed that better explained

the new observations.

How Did Thomson Contribute to Atomic Theory?In 1897, a British scientist named J. J. Thomson was working with cathode rays,

mysterious rays in vacuum tubes. His experiments helped scientists better understand the structureof atoms. In his experiments, Thomson used a vacuum tube that contained two electrodes. One

electrode, called the cathode, was negatively charged. The other, called the anode, was positively

charged. When electricity was sent through the tube, a glowing beam appeared inside the tube.

Other scientists had shown that this beam came from the cathode. However, they had not been able

to determine what the beam was made of. When Thomson placed a magnet near the tube, the beam

was deflected, or bent, as shown in the figure below. Only streams of charged particles can be bent

by a magnet. Light rays cannot. Therefore, Thomsons experiment suggested that cathode rays

were actually streams of tiny, charged particles.

Based on the direction the beam bent, Thomson determined that the particles in the beam

were negatively charged. His experiments also showed that, no matter what substance the cathode

was made of, the beam was always the same. Based on his results, Thomson concluded that the

particles in the beam came from atoms. He also concluded that the particles were the same in

atoms of different elements. This is how Thomson discovered electrons, the negatively charged

particles inside an atom.


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THOMSONS MODEL OF THE ATOM

Thomsons experiment showed that atoms contained even smaller particles. He proposed a new

model of the atom based on his discovery. According to Thomsons model, electrons were spread

randomly throughout an atom. The rest of the atom was a positively charged material. The

electrons floated in the positively charged material.

How Did Rutherford Contribute to Atomic Theory?

According to Thomsons atomic theory, the mass of an atom was spread evenly throughout

its volume. Ernest Rutherford, a former student of Thomsons, developed experiments to test this

idea. In one experiment, Rutherfords students aimed a beam of positively charged particles at a

very thin sheet of gold foil. Rutherford predicted that the positive charge in the gold atoms would

be too weak to affect the positively charged particles. Therefore, the particles would either passstraight through the foil or be deflected slightly. However, this is not what the experiment showed.

Most of the particles passed straight through the foil. Some were deflected slightly. However,

some of the particles bounced back at sharp angles. These results are shown in the figure below.


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RUTHERFORDS MODEL OF THE ATOM

The results ofRutherfords experiment were very surprising. In his notebook, Rutherford

wrote, It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it

came back and hit you. However, further experiments produced the same results. Therefore,

Rutherfords results were confirmed. Rutherford concluded that the sharply reflected particles

collided with dense parts of the atoms in the gold foil. The particles bounced back because theyhad the same charge as the dense parts of the atom. Because so few particles bounced back at sharp

angles, Rutherford concluded that these dense parts must be very tiny. Based on his results,

Rutherford concluded that an atoms positive charge is concentrated at the center ofthe atom. This

positively charged, dense core of the atom is called the nucleus (plural, nuclei). Data from the

experiments showed that the nucleus must be very tiny. If an atom were the size of a football

stadium, its nucleus would be only as big as a marble. Rutherfords results led to a new model of

the atom. In the Rutherford model, negatively charged electrons orbit the positively charged

nucleus, as shown below. This is similar to the way that the planets orbit the sun.

BOHRS MODEL OF THE ATOMIn 1913, Niels Bohr was suggesting an atom model that able be explained through hydrogen

spektra. He accept this concept such as those which proposed by Rutherford , however by applying

quantum theory radiasi such as those which developed by Planck and of Einstein in explaining the

nature of electron planet system.


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The Bohr postulates

a. Electrons in an atom to orbit around the nucleus in orbit particular. Each orbit has a specific

energy level and energy an electron is fixed at while in orbit. Electron who are at this level is called

the stationary and any energy levels called energy levels or the skin. electrons in energy level does

not radiate energy.

Figure 12. Bohr Atom Model

b. Emission and absorption of energy in the form of radiation can only be generated if an electron

moving from the stationary to the other levels.

c. No energy is emitted or absorbed slowly, but in units / h package? (called a quantum), where h is

a constant Planck and? frequency energy is radiated.

d. Furthermore the energy levels of the nucleus, the more energy too. Energy is absorbed when an

electron jumps from orbit part in the the outer orbit. Energy will be emitted when electrons move

from an outer orbit to orbit deeper.

e. Energy in each orbit is affected by the conditions in which angular momentum (MVR) electrons

moving in its orbit has a particular value that is simply a multiple of of h / 2? .

With m = mass of the electron, v = velocity, r = radius of orbit, h =

Planck constant, and = orbit occupied by electrons (1, 2, 3, ...... or corresponding letters K, L, M,

....... ).


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MODREN ATOMIC THEORY

In 1924, Louis de Broglie physicist France winner Nobel prize in 1929, concluded that the

electrons in the atom can be seen as a particle and a wave. as a result of dualistic nature of the

electron, Heisenberg nobel prize winner for the field physics in 1926 put forward the principle of

uncertainty, which is not impossible to know simultaneously the position and velocity electrons.

For this reason the electron trajectory is described Bohr not exist. That can be said is the electronsin the atom probability have found in certain spaces in called atomic orbitals. The idea that

electrons are in orbitals around the nucleus of an atom is the atomic model

edge.

In 1926, a physicist Erwin Schrodinger Austria Nobel prize winner for physics in 1933,

successfully formulate the wave equation to describe the motion electrons in the atom. Energy and

geometrical orbitals as we have learned, derived by calculations using the Schrodinger wave

equation.


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ATOMIC SYMBOLS

Atomic symbols are a symbolic way for people to refer to elements in the periodic table.

For instance, the box on the top left contains information about the simplest chemical element,

hydrogen. The symbol of this element is H.

Note: The atomic symbol is made up of the first letter of the word

hydrogen. This is not always the case. The element helium must use

the first two letters in its name to avoid confusion. The first letter is

always capitalized and the second letter is always lower case.

Lithium is third element shown on the table with an atomic symbol Li. Using this same

system it would seem that lead would be Le. However, lead has the atomic symbol Pb which

stands for the Latin word for lead which is plumbum.

ATOMIC NUMBERS

The number that is in the upper left hand side of the box for lead is the atomic number for

this element. In this case, lead has an atomic number of 82. Atomic numbers represent the number

of protons in one atom of the element. Therefore, each lead atom has 82 protons in its nucleus. Theterm periodic refers to trends in values that change in a regular pattern from left to right across a

row and from top to bottom down a column of the periodic table. For instance, the second row .

across the periodic table contains the elements lithium, beryllium, boron, carbon, nitrogen,

oxygen, fluorine, and neon. Their symbols are Li, Be, B, C, N, O, F, and Ne. From left to right,

their atomic numbers increase from three to ten, meaning that lithium atoms have three protons,

beryllium atoms have four, and so on, up to neons ten.

ISOTPES AND ATOMIC SYMBOLS


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The atom of each element is made up of electrons, protons and neutrons. All atoms of the

same neutral element have the same number of protons and electrons but the number of neutrons

can differ. Atoms of the same element but different neutrons are called isotopes. Because of these

isotopes it becomes necessary to develop a notation to distinguish one isotope from another - the

atomic symbol. The atomic symbol has three parts to it:

1. The symbol X: the usual element symbol2. The atomic number A: equal to the number of protons (placed as a left subscript)3. The mass number Z: equal to the number of protons and neutrons in the isotope

(placed as a left superscript)


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IsotopesAn atom is defined as a small particle that makes up most types of matter. Atoms are so

small it would take about 1 million of them lined up in a row to equal the thickness of a human

hair. Atoms are made up of even smaller particles. The largest of these particles are protons,

neutrons and electrons. The identity of a type of matter depends on the number of protons in the

nucleus of an atom of that type of matter. All atoms of the same type of matter have the same

number ofProtons in the nucleus. For example, all carbon atoms have six protons. Not all atoms of the

same type of matter have the same number of neutrons. Most carbon atoms have 6 neutrons,

although some have more and some have less. Atoms of the same type of matter that have different

numbers of neutrons are called isotopes. Most types of matter have isotopes. The atomic mass, or

mass number, can be used to identify isotopes. The mass number of a type of matter is the number

of protons and neutrons in one atom of that matter. In our example of carbon, 6 protons + 6

neutrons = 12 particles in the nucleus; the mass number = 12. The name for this isotope is Carbon

12. The symbol for Carbon12 is:

Diagrams of carbon isotopes:

Elements occur in nature as mixtures of isotopes.


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General Idea

The atomic orbitals (AO) are theoretical regions around the nucleus where the probabilityof finding an electron is high.

The covalent bind involves a sharing of electrons. This bond between two atoms is an

overlap of two atomic orbitals.

The overlap of two AO forms two MO-one bonding MO (lower energy) and one

antibonding MO (higher energy).

The hybridization of AO involves a mixing of AO on an atom to create a hybrid AO. These

new hybrid AO allow for greater overlap when forming MO. The hybridization determines

the shape of the molecule.

Atomic Orbitalss orbital: Spherically symmetric about the nucleus

p orbital: Dumbbell shapeds orbital

S orbitals are spherical space shows no particular direction because the probability of electrons are

found in this form is the same in all directions away from the nucleus.

The nucleus is located on the center of the ball. Consider drawing direction s orbital space below!

Greatest probability of finding the electron in the s orbital present in the area around the ball,

which is to orbital:

a. 1s: contained in a spherical shell

b. 2s: there is a second layer in the cloud

c. 3s: located on the third layer of the cloud

Probability of orbital picture found on each skin:

FORMS OF ORBITAL


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These figures are similar to cake onde-onde. This cake-shaped ball in which there is also content

with a spherical shape. Can you describe the cake like this?

What about the p subshell?

P subshell consists of three p orbitals. Because the value of the magnetic quantum number three is

-1, 0, and +1. The three orbital has the same energy but the direction of each space is different.Taken together, these three orbitals are mutually perpendicular to each other. When depicted on a

Cartesian coordinate system with axes X, Y, and Z the p orbitals are located on the X-axis is called

the orbital PX, while located on the Y axis is called orbital PY. Similarly, the p orbitals that lie in

the Z-axis is called the orbital PZ.

Can you imagine such an explanation?

Figure 7. Forms of Orbital - orbital PX, PY, PZ

So the picture of the p orbitals with azimuthal quantum numbers l = 1 is expressed in the following

picture!Well, look at the picture below!

Figure 8. P orbital shape

Can you imagine the p orbital images?

If you can not imagine, then try to make the p orbitals with balloons! Follow the instructions below

manufacturing.

Take 3 pieces of balloons. Then gyre (play) at the center of the balloon. Do this on all the balloons.

Prepare your straps will be used to combine all three balloons. First you put the balloon upright

(vertical), while the second balloon you put the flat (horizontal), and third balloon you put the

balloon between the first and second balloons. Part twisted balloons should be in the middle bond

of the three balloons tied together. Make sure that the three balloon is tied firmly. Show what you

make it to the teacher coached. Now, can you imagine that's already orbital shapes p. Balloons as

orbital (where the possibility of finding an electron) while the balloon is twisted nuclei.


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D subshell consists of five d orbitals because the value of -2, -1, 0, +1, +2. Like the p orbitals, d

orbitals also have the same energy but the direction of each space is different. When depicted on

the third Cartesian coordinate sisitem d orbitals occupy the space between the axes in the Cartesian

coordinate. Each orbital is expressed as the DXY, DXZ and dYZ, while the other two d orbitals

located on the axis of a Cartesian coordinate of each orbital is expressed as dx2-Y2 and dZ2. Form

five d orbitals can be described as follows:

Orbital dZ2 lies in Z axis

Orbital dx2-Y

2is located on the X and Y

Orbital DXY located between the X and Y

Orbital DXZ located between the X and Z

Orbital dYZ located between Y and Z axis

While the f orbitals have 7 orbitals as illustrated as follows:


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The Quantum NumbersThe theory of quantum mechanics tells us that in an atom, the electrons are found inorbitals, and each orbital has a characteristic energy. Orbital means "small orbit". We are

interested in two properties of orbitals - their energies and their shapes. Their energies are

important because we normally find atoms in their most stable states, which we call their

ground states, in which electrons are at their lowest possible energies.

The Principal Quantum Number , n

The quantum number n is called the principle quantum number. You already know this as

shell. The shell "K" has been given the value n = 1, the "L" shell has been given the value n

= 2.

n 1 2 3 4 ...shell K L M N ...

The principle quantum number serves to determine the size of the orbital, or how far the

electron extends from the nucleus. The higher the value ofn the further from the nucleus

we can expect to find it. As n increases so does the energy required as well because the

further out from the nucleus you go the more energy the electron must have to stay in

orbit. Bohr's work took into account only this first principle quantum number. His theory

worked for hydrogen because hydrogen just happens to be the one element in which all

orbitals having the same value of n also have the same energy. Bohr's theory failed for

atoms other than hydrogen, however, because orbitals with the same value ofn can have

different energies when the atom has more than one electron.

The Secondary Quantum Number, l

The secondary quantum number, l, divides the shells up into smaller groups of

subshells called orbitals. The value ofn determines the possible values for l. For any given

shell the number of subshells can be found by l = n -1. This means that for n = 1, the first

shell, there is only l = 1-1 = 0 subshells. ie. the shell and subshell are identical. When n = 2

there are two sets of subshells; l = 1 and l = 0. A number could be used to identify the

subshell however to avoid confusion between the numerical values ofn and those ofl the l

values are given a letter code.

value of l 0 1 2 3 4 .....

letter designation s p d f g .....

To designate a particular subshell we write the number of the shell itself followed by the

subshell designator.

n l This illustrates the relationship between "n" and "l".

1 s the first shell has one orbital type associated with it.

2 s p the second shell has two orbital types associated with it.

3 s p d etc

4 s p d f

5 s p d f g

The principle quantum number describes size and energy, but the second quantum number

QUANTUM NUMBERS


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describes shape. The subshells in any given orbital differ slightly in energy, with the energy

in the subshell increasing with increasing l. This means that within a given shell, the s

subshell is lowest in energy, p is the next lowest, followed by d, then f, and so on. For

example:

4s < 4p < 4d < 4f ---> increasing energy

The Magnetic Quantum Number, ml

The third quantum number, ml, is known as the magnetic quantum number. It splits the

subshells into individual orbitals. This orbital describes how an orbital is orientated in

space relative to other orbitals. i.e. It gives 3D information. The first "s" subshell has a

magentic number of "1". The "p" subshell has a magnetic number of "3". A simple

numeric progression gives us:

s p d f


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In general, the number of electrons in a shell is 2n .

shell number of subshells maximum number of electrons

1 1s 2

2 2s 2p 8

3 3s 3p 3d 18

4 4s 4p 4d 4f 32

Orbital Filling Rules

1. Aufbau/Build-up Principle

Lower energy levels fill before higher energy levels. Orbital fulfill lower energy level is 1s

and continued by 2s, 2p, 3s, 3p and etc

Atom of H : have 1 electron, and the configuration is 1s1

Atom of C : have 6 electron, and the configuration is 1s2

2s2

2p2

Atom of K : have 19 electron, and the configuration is 1s2

2s2

2p6

3S2

3p6

4s1

2. Pauli Exclusion Principle

No two electrons can have the same 4 quantum numbers An orbital has a maximum of 2

electrons of opposite spin

3. Hunds Rule

Electrons only pair after all orbitals at an energy level have 1 electron


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Handout Struktur Atom Finall

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