2016 Topic 2: Atomic Structure

Atomic

Structure

IB Chemistry Power Points

Topic 02

Atomic Structure

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Review – Basic Atomic Structure

NUCLEUS ELECTRONS

PROTONS NEUTRONS

POSITIVE

CHARGE

ATOM

POSITIVE

CHARGE

PROTONS

NEUTRAL

CHARGE

NEUTRONS

NUCLEUS

NEGATIVE CHARGE

ELECTRONS

ATOM

Subatomic

components

Relative

Mass

Charge

Proton1 +1

Neutron1 0

Electron5 x 10-4 -1

Review – Basic Atomic Model

A-Z notation

© Addison-Wesley Publishing Company, Inc.

12

6 Cmass number A

atomic number Z

element symbol

The atomic number

equals the number of

protons. Each element

has a unique atomic

number.

Mass Number

• mass number A = protons + neutrons

• always a whole number


• NOT the value given on

the Periodic Table!

Practice: determine the required values and

write the chemical symbol in A-Z notation.

• Chlorine-37

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

17

20

Cl37

17

Ions

• ions are electrically charged atoms

Neutral atom

negative ionpositive ion

lose electrons gain electrons

p+ > e- p+ < e-

cation anion

Practice: determine the required values for

the negative chloride ion 37 Cl -1

37 Cl-1

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

18

20

Practice: determine the required values for

the positive calcium ion 40 Ca +2

40 Ca+2

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

20

40

20

18

20


Isotopes: Atoms of the same element with different

mass numbers.

carbon-12 and

carbon-14 are

isotopes

similar chemical properties

stable

radioactive

Radioisotopes and Their Uses

Radioisotopes are unstable isotopes that undergo

radioactive decay. Radioisotopes have a number

of uses:

U-235 is used as fuel in nuclear reactors

Co-60 is used in cancer radiation therapy

C-14 is used as a tracer and for archeological

dating

Am-241 is used in smoke detectors

Mass SpectrometerA mass spectrometer is used to detect, identify and

measure the abundance of different atoms,

molecules or molecular fragments.

Mass spectrometer studies are used to determine

the average atomic mass for an element. The

operation of a mass spectrometer can be divided

into 5 steps:

1. Vaporization

2. Ionization

3. Acceleration

4. Deflection

5. Detection

Chapter 12 13=>

Vaporization: the element to be analyzed is heated and vaporized

(gaseous form).

http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html


Chapter 12 14=>

Ionization: the gaseous element is injected slowly into a vacuum

chamber where the atoms are bombarded by electrons. This

forms ions positive ions X (g) + e- X

+(g) + 2 e

-



Chapter 12 15=>

Acceleration: the gaseous ions are accelerated through an

electric field (towards a negative plate)



Chapter 12 16=>

Deflection: Ions are deflected in an adjustable magnetic field

oriented at right angles to the path. Heavier ions are deflected

less.



Chapter 12 17=>

Detection: ions of a specific mass are counted



A sample mass spectrograph

Output provides

the abundances of

the elemental

isotopes of

different relative

mass

Atomic Mass is Relative

• 12C atom = 1.992 × 10-23 g

• 1 p = 1.007276 amu

1 n = 1.008665 amu

1 e- = 0.0005486 amu


• atomic mass unit (amu)

• 1 amu = 1/12 the mass of a 12C atom

Average Relative Atomic Mass AR

• a weighted average of

all isotopes of an

element

100

(%)(mass(mass)(%) )

Avg.

Atomic

Mass

• this value is found on the Periodic Table

• based on the %

abundance data from

mass spectrometer

Avg.

Atomic

Mass


• EXAMPLE: Calculate the average atomic mass of

chlorine if its abundance in nature is 75.77% 35Cl, and 24.23% 37Cl.

(35)(75.77) (37)(24.23)

10035.48

amu


equation 1

equation 2

(68.9257)(x) (70.9249)(y)69.7231=

100

x + y = 100

Average relative mass of Ga 69.7231 amu

Gallium has two naturally occurring isotopes, Ga-

69 and Ga-71, with masses of 68.9257 amu and

70.9249 amu, respectively. Calculate the percent

abundances of these isotopes

Solve to get 60.1% Ga-69 and 39.9% Ga-71

All EM radiation is fundamentally the same. The

only difference between a gamma ray and a

radio wave is the frequency/wavelength/energy.

Visible light is one category of EM radiation. The

visible light spectrum is subdivided into six

“colors”.

White LightPrism

RED

ORANGE

YELLOW

GREEN

BLUE

VIOLET

A continuous spectrum includes all wavelengths of radiation in a given range.

When white light is passed through a prism a continuous spectrum is produced.

Colored lights do not emit all the wavelengths of the

visible light spectrum. For example, a red light emits

mostly wavelengths from the red end of the spectrum.

An energized gas sample will emit light of specific

wavelengths characteristic of the gas. This is called a line

spectrum

Emission spectra are unique for each element

Balmer Lyman

The Bohr model of the atom was developed using information from hydrogen emission spectrum studies. Bohr envisioned an atomic model with:

• a central dense positive nucleus composed of protons and neutrons.

• negative electrons at specific energies orbit the nucleus

• mostly empty space. Nucleus is 10-5 times smaller than atom.

Bohr further stated that the orbiting electrons occupy discrete energy levels. Electrons can only “jump” between energy levels if they absorb or emit a specific amount of energy.

Bohr saw the line spectrum of hydrogen as a direct result of energized electrons releasing a specific amount of energy by emitting a photon of light at a certain wavelength.

The different lines in the hydrogen spectrum were evidence for a number of different energy levels.

lower energy

longer wavelength

higher energy

shorter wavelength

Visible spectrum for

hydrogen atomconvergence

Lower energy = more stable electron orbit

Electrons will first occupy the lowest energy level orbital (Aufbau principle).

Each energy level has a maximum possible number of electrons.

As you should recall:

1st energy level (ground state) = 2 electrons

2nd energy level = 8 electrons

3rd energy level = 8 electrons

A carbon atom has six electrons

1st energy level holds 2

2nd energy level takes the remaining 4

The electron configuration for carbon would be written as 2,4

The electrons in the outermost energy level are called valence electrons. Carbon has 4 valence electrons.

Try writing the electron configuration for calcium

A calcium atom has 20 electrons

1st energy level holds 2

2nd energy level holds 8

3rd energy level holds 8

4th energy level holds last 2

The electron configuration for calcium would be written as 2,8,8,2

Connect to Periodic Table

1

2

3

4

EnergyLevel

2016 Topic 2: Atomic Structure

Education

Transcript of 2016 Topic 2: Atomic Structure