1

Atomic Structure

Atoms and Matter

Democritus proposed

that atoms are tiny,

Indivisible particles that

make up all matter

The word ‘atom’ means

unable to be divided.

Thomson’s Atomic model(1898) (Plum-pudding model)

How do we know the structure of

an atom?

• Rutherford (1911) bombarded Alpha particles (Helium particles) on a very thin gold foil.

• Most of the particles passed through, some deflected at large angles

• 1 in 20000 deflected back to its own path.

What Rutherford’s experiment told us…

• Most of the atom is empty space.

• There is a very tiny dense core of mass and + charge located in the atom. (Called nucleus)

Rutherford’s Atomic model (1920)

• The atom is mostly

hollow.

• The mass and a positive

charge are located at

the center in a very

small portion.

• Negatively charged

particles revolve around

the center like the

planets revolve around

the sun.

7

Photo May, 2013

•First Ever picture of Hydrogen Atom! • Taken with a quantum microscope

http://io9.com/the-first-image-ever-of-a-hydrogen-atoms-orbital-struc-509684901

8

The 3 sub-atomic particles that make up an atom

Protons

Neutrons

Electrons

9

Proton Facts

• # of protons = the atomic number

• Positively Charged

• Unique to each element, its the identity of an element.

• No two elements can have the same atomic number

• When the number of protons changes, it is no longer the same element

10

Electron Facts

• Negatively charged

• Normally, there are equal number of protons and electrons in an atom

• This means the atom as a whole is neutral in charge (neither positive or negative)

11

Electron Facts

• When you change the number of electrons in an atom, you upset the balance between protons and electrons giving the atom a positive or negative charge

• IF YOU CHANGE THE NUMBER OF ELECTRONS, YOUR DON’T CHANGE THE ELEMENT, YOU JUST GIVE IT A CHARGE

12

Neutron Facts

• Neutron numbers have to be calculated from the periodic table. • (Mass #– Atomic #) **more on this later…

• They have no charge (neutral)

Mass #

Atomic #

13

WHAT IS AN ATOM? UNTIL 4:20

Take 2, take 3…

• Take 2 minutes to review your notes and, highlight the important points of the lesson so far.

• Take 3 minutes to turn to your table partner and share with them what you highlighted

14

15

Location of Subatomic Particles in the Atom

• Protons and Neutrons reside in the

nucleus

Location of Subatomic Particles in the Atom

16

• Electrons – reside outside nucleus

in “shells”

Using Models

• 3-D Diagram • Flattened Diagram (click below)

18

Mass of sub atomic particles

Particle Charge Location

Relative Mass

(atomic mass

unit – amu)

Proton + (positive) nucleus 1 amu

Neutron No charge –

neutral nucleus 1 amu

Electron

- (negative)

Outside of

nucleus in

shells

.005 amu

99.9% of the mass of an atom is in the nucleus

1 amu = 1.66053892 × 10-27 kilograms

Atomic Structure Layered Book

19

20

Symbol of an atom (element)

21

22

Where in this symbol can you find the chemical symbol, atomic number and mass number?

Guesses?

Atomic Weight/Mass Number

Atomic Number

(# of protons)

Element Symbol

23

Multiple ways, mean the same

24

Atomic number

• Atomic number

The number of protons in an

atom

• For an atom,

# of protons = # of electrons

# of electrons/# of protons /atomic number

25

Mass number

• Mass number

= # of protons + # of neutrons

• To calculate # of Neutrons

= Mass number – Atomic number (# of protons)

Mass number = # of protons + # of neutrons

26

You Try It Given , (a) What is the number of protons? Ans: 29 (b) What is the number of electrons in Cu

atom? Ans: 29 (c) What is the mass number? Ans: 64 (d) What is the number of neutrons? Ans: 64-29=35

Cu64

29

27

IONS

• An atom that has a positive or a negative charge due to the LOSS or GAIN of an electron

• An ION is an atom or compound with a positive or a negative charge

• EXAMPLE • Na+ - called an CATION due to a loss of an

electron • Cl- - called a ANION due to a gain of an

electron

28

IONS – You Try it

Na gives away 1 electron. What would its charge be? F steals an electron. What would its charge be?

29

You Try It

Electrons, Protons and Neutrons…OH MY! Atomic structure!

30

Neutron Facts

• All elements, naturally occurring, have some atoms that have more or less neutrons than what is reported on the periodic table.

• Atoms within the same element that have a

different number of neutrons are called ISOTOPES

31

ISOTOPES • Atoms with the same number of protons, but

DIFFERENT number of neutrons

• Still the SAME element (because the number of protons doesn’t change)!

32

ISOTOPES

• Due to the differing number of NEUTRONS, the mass of each ISOTOPE will be different

• He-1 • He-2 • He-3

33

You Try it: Isotopes

34

BAG O’ ISOTOPES

35

Electronic Structure

• The way the electrons are arranged is called its electronic structure

• Electrons are arranged in shells which are numbered from the nucleus outwards

• Each shell is capable of holding up to a certain number of electrons

36

The HOME of Electrons

• Electrons live in shells. • Only so many electrons can live in each shell

Shells

37

Electronic Structure

• Electrons are arranged in shells which are numbered: 1, 2, 3, 4 from the nucleus onwards

Shell no. Maximum no. of electrons

Name

1 2 Duplet

2 8 Octet

3 8

(for atoms with proton number

20)

Octet

38

Electronic Structure

1st shell 2 electrons

3rd shell

8 electrons

(proton number 20)

Nucleus

2nd shell

8 electrons

39

Maximum # of electrons 1stshell

1st shell – max. 2 electrons 2nd shell – max. 8 electrons 3rd shell – max. 8 electrons 4th shell – variable LAST SHELL – Max of 8

nucleus

40

Electronic Structure To find the electronic configuration of an atom, we should (1) Fill the electrons into the shell nearest to the nucleus first. This shell can take a maximum of 2 electrons (2) Once this shell is filled, the electrons go to the next available shell which has a maximum capacity of 8 electrons, and so on

41

Electronic Structure

Sodium,

Na23

11 Electronic

Configuration

2, 8, 1

1st shell

2nd shell

3rd shell

Na

You Try It • Draw the electron structure (electron dot, lewis dot) for • Lithium

• Carbon

• Calcium

42

43

Valence Electrons

Shells

• Electrons will keep filling shells until all the electrons have a ‘home’

• If an atom has 11 electrons, 2 will fill the 1st shell, 8 will fill the 2nd and 1 will fill the 3rd. This last electron is called the Valence electron

44

Electron Dot Diagrams Bohr model vs. Lewis Dot

45

You Try it: Electron Dot Diagrams

Classification of Matter

Composition of Matter

MATTER

Elements, Molecules, Compounds,

Solutions

Element – composed of identical atoms

Molecule - when two or more atoms join together chemically

Compound – a molecule that contains at least two different elements. A fixed amount

Solution – variable combination of two or more elements

• Element

• matter composed of identical atoms

• All atoms are the same

• EX: copper

• Molecule

• Composed of identical elements

• Ex. Oxygen

49

• Compound

• composed of 2 or more

elements in a fixed ratio

• properties differ from those

of individual elements

• EX: salt (NaCl)

Solution (Mixture)

• Variable combination of 2 or more pure

substances.

Homogeneous Mixture (Solution)

even distribution of components

very small particles

particles never settle

EX: saline solution, fresh pickle juice

Mixtures

• Heterogeneous Mixture

• uneven distribution of components

• colloids and suspensions

• EX: granite

Mixtures

• Colloid

• medium-sized particles

• Looks cloudy

• particles never settle

• EX: milk, fog

Mixtures

• Suspension

• large particles

• particles scatter light

• particles will settle

(needs to be shaken)

• EX: Italian salad dressing

(oil, vinegar, and spices)