Structure of the Atom

Introductory Chemistry

Atomic Structure

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Atoms are tiny particles!!

NUCLEUS ELECTRONS

PROTONS NEUTRONS

POSITIVE

CHARGE

ATOM

POSITIVECHARGE

PROTONS

NEUTRALCHARGE

NEUTRONS

NUCLEUS

NEGATIVE CHARGE

ELECTRONS

ATOM

Mostly empty space!!

An atom consists of • a nucleus (of protons and neutrons) • electrons in space about the

nucleus.

The Anatomy of an Atom

Nucleus

Electron cloud

Subatomic

components

Relative Mass

Charge

nucleus

Proton 1 +1

Neutron

1 0

Orbital

cloud

Electron

0.005 -1

Features of the Atom

A-Z notation

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126C

mass 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

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• NOT the value given on the Periodic Table!

Atomic Number• atomic number z = protons

• always a whole number

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• identifies the element

Practice: Lithium has the atomic number 3 and mass number 7

– # of protons:

– # of neutrons:

– # of electrons:

3

4

3

Practice: Lithium has the atomic number 3 and mass number 7

– electron arrangement

(configuration)

2, 1

Lithium is in Group 1 on the Periodic Table

Practice: electron arrangements of the first 20 elements (2,8,8,2)

• Chlorine-37– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

17

20

Cl3717

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 positive calcium ion 41

Ca +2

41 Ca+2

– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

20

41

20

18

21

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Isotopes: Atoms of the same element with different mass numbers.

carbon-12 and carbon-14 are

isotopes

similar chemical properties

stable

radioactive

Average Relative Atomic Mass AR

• a weighted average of all isotopes of an element

100

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

Avg.AtomicMass

• this value is found on the Periodic Table

• based on the % abundance data from mass spectrometer

Average Relative Atomic Mass AR or RAM

What is the relative atomic mass of chlorine?

Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37. 75% of chlorine atoms are 35Cl.

What % of chlorine atoms is 37Cl?

Average Relative Atomic Mass AR or RAM

What is the relative atomic mass of chlorine?

Chlorine has two naturally occurring isotopes, Cl-35 and Cl-37. 75% of chlorine atoms are 35Cl.

What % of chlorine atoms is 37Cl?

Avg.Atomic =

Mass

Another way of looking at it

Mass Number of IsotopeOut of 100 atoms, how many have this mass?

What would be the total mass of these atoms?

35Cl37Cl

Another way of looking at it

Mass Number of IsotopeOut of 100 atoms, how many have this mass?

What would be the total mass of these atoms?

35Cl 7537Cl 25

Another way of looking at it

Mass Number of IsotopeOut of 100 atoms, how many have this mass?

What would be the total mass of these atoms?

35Cl 75 35 = 2625

37Cl 25 37 = 925

Another way of looking at it

Mass Number of IsotopeOut of 100 atoms, how many have this mass?

What would be the total mass of these atoms?

35Cl 75 35 = 2625

37Cl 25 37 = 925

Total mass of 100 atoms 3550

Another way of looking at it

Mass Number of IsotopeOut of 100 atoms, how many have this mass?

What would be the total mass of these atoms?

35Cl 75 35 = 2625

37Cl 25 37 = 925

Total mass of 100 atoms 3550

Average mass of 1 atom 35.5