How Many Electrons

• The atoms of any element have an equal number of protons and electrons.

Atom Protons Neutrons Electrons

Helium 2 2 2

Copper 29 35 29

Cobalt 27 32 27

Iodine 53 74 53

Germanium 32 41 32

..and so overall charge equals zero

How Many Electrons

• Fill in the blank columns

Atom Protons Neutrons Electrons Atomic number

Mass Number

Boron 5 6

Potassium 19 20

Chromium 24 28

Mercury 80 121

Argon 18 22

5 5 11

19 19 39

24 24 52

80 80 201

18 18 40

Note – atomic number is defined as the number of protons rather than electrons because atoms can lose (or gain)

electrons but do not normally lose protons

Activity

ActivityDrag the statements at the top onto the correct

side of the table

ActivityDrag the statements at the top onto the correct

side of the table

How Are Electrons Arranged?• Electrons are not evenly spread.• The exist in layers known as shells.• The arrangement of electrons in these shells is

often called the electron configurationelectron configuration..

2nd Shell

1st Shell

3rd Shell

4th Shell

How Many Electrons per Shell?• Each shell has a maximum number of

electrons that it can hold.

1st Shell: 2 electrons

2nd Shell: 8 electrons

3rd Shell: 8 electrons

The maximum

Working Out Electron Arrangements

1. How many electrons do the element atoms have? (This will equal the atomic number).

2. Draw them into the shells working outwards until you have used them all up.

1st Shell: Fills this first

2nd Shell: Fill this next

Drawing neat diagrams helps you

keep track!

The Electrons in Carbon

The Electrons in Neon

The Electrons in Silicon

Electrons in Phosphorus

The Electrons in Argon

The Electrons in Sodium

The Electrons in Fluorine

The Electrons in Aluminium

The Electrons in Nitrogen

The Electrons in Sulfur

The Electrons in Oxygen

The Electrons in Chlorine

The Electrons in Magnesium

Happiness is…………………. A full outer shell

1+ ion ProtonsElectrons

1- ion ProtonsElectrons

Ions and Electron Structures

1. Ions are atoms that have either extra electrons added or electrons removed. e.g.

Atoms ProtonsElectrons

Lose 1 electron Gain 1 electron

So in ions the number of

electrons no longer equals the

number

of protons

• These are ions formed by the atom losinglosing one or more electrons.

• They are called cationscations. This is because during electrolysis they move towards the cathode. (Or because they are “pussytive”!).

• The charge on the ions is equal to the number of equal to the number of electrons that the atom has lostelectrons that the atom has lost.

• In equations the charge is usually shown above and to the right of the symbol. (E.g. Mg2+ ).

Positive Ions

Lost 1 e- +

Lost 2 e- 2+

Lost 3 e- 3+

It is nearly always metal

atoms that lose

electrons

Ions usually have

OUTER electron

shells that are either completely full or else

empty

Na Bye!

The Electrons in a Sodium IonIn the sodium atomatomAtomic number = number of protons = 11 Number of electrons = 11

Electron arrangement: 2.8.1 (Incomplete Shell)

Na+

Electron lost

Electron arrangement: 2.8 (Full Shells)

23

Na11

Mg

The Electrons in a Magnesium Ion

In the magnesium atomatomAtomic number = number of protons = 12 Number of electrons = 12

Electron arrangement = 2.8.2 (Incomplete shell)

Mg2+

Electron arrangement 2.8 (Full Shells)

Bye!

Bye!

2 electrons lost

24

Mg12

The Lithium Ion

Li

3

2

1

1st Shell = 2: full

2nd Shell = 1: not full

2.1

1

•How many electrons?

•How many electrons in the first shell?

•How many electrons in the second shell?

What electron arrangement?

How many electrons to lose?

New electron arrangement? Include a diagram

2.(0)

Bye!Li+

7

Li3

Activity

The Boron Ion

B

5

2

3

1st Shell = 2: full

2nd Shell = 3: not full

2.3

3

•How many electrons?

•How many electrons in the first shell?

•How many electrons in the second shell?

What electron arrangement?

How many electrons to lose?

New electron arrangement? 2.(0)

Bye!

Bye!

Bye!

B3+

11

B5

Activity

• These are ions formed by the atom gaininggaining one or more electrons.

• They are called anionsanions. This is because during electrolysis they move towards the anode.

• The charge on the ions is equal to the number of equal to the number of electrons that the atom has gainedelectrons that the atom has gained.

• In equations the charge is usually shown above and to the right of the symbol. (E.g.. O2- ).

Negative Ions.

Gain 1 e- -

Gain 2 e- 2-

Gain 3 e- 3-

It is nearly always

non-metal atoms that

gain electrons

Ions usually have

OUTER electron

shells that are either completely full or else

empty

The Electrons in a Sulphide Ion.In the sulphur atomatomAtomic number = number of protons = 16 Number of electrons = 16

Electron arrangement: 2.8.6 (incomplete shell)

Electron arrangement 2.8.8 (Full shells)

2 electrons gained

S S2-

32

S16

The Electrons in a Fluoride Ion.

In the fluorine atomatomAtomic number = number of protons = 9 Number of electrons = 9

Electron arrangement: 2.8.7 (incomplete shell)

Electron arrangement 2.8.8 (Full shells)

1 electron gained

F F2-

19

F9

The Oxide Ion16

O8

O

8

2

6

1st Shell = 2: full

2nd Shell = 6: not full

2.6

2

•How many electrons?

•How many electrons in the first shell?

•How many electrons in the second shell?

What electron arrangement?

How many electrons to gain?

New electron arrangement? 2.8

O2-

Activity

Drag the words at the top to their correct places in the sentences.

Word check

1. Which of the following is not a sub-atomic particle?

A. Proton.

B. Isotope.

C. Neutron.

D. Electron.

2. The element Cobalt has a relative atomic mass of 59 and an atomic number of 27. Which of these is a true statement about each neutral cobalt atom?

A. It contains 59 neutrons.

B. It contains 27 electrons.

C. It contains 32 protons.

D. It contains equal numbers of neutrons and electrons.

3. The Periodic Table displays iron as shown below. This indicates that Fe atoms:

A. contain 56 neutrons.

B. contain 30 electrons.

C. contain 26 protons.

D. contains more protons than neutrons.

56

Fe26

4. Bromine consists of a mixture of two isotopes: Bromine-79 and Bromine-81

• Which of the following is true:

A. Both isotopes contain 35 protons.

B. Bromine 79 contains 46 neutrons.

C. Bromine 81 contains 44 neutrons.

D. Bromine-81 is more reactive than bromine-79.

80Br35

5. Natural boron consists of approx. 20% boron-10 and 80% boron-11.

• What will the relative atomic mass of natural boron will be?

A. 10.0

B. 11.0

C. 10.5

D. 10.8

?B5

6. Which answer best describes the shell arrangement of the electrons in a sodium atom?

A. 2,8,1.

B. 2,2,7.

C. 2,8,8,3.

D. 2,8,8,1.

23Na11

7. Which answer best describes the shell arrangement of the electrons in an oxygen atom?

A. 2,8,6.

B. 2,8,8.

C. 2,8.

D. 2,6.

16O8

8. Which of these elements will have electron shells that are either full or empty (i.e. not partially full)?

14N7

A 40Ar18

B

40Ca20

C 27Al13

D

9. Which answer best describes the shell arrangement of the electrons in an oxide ion O2-?

A. 2,8,6.

B. 2,8,8.

C. 2,8.

D. 2,6.

16O8