Atomic Structure…

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The Nucleus

The Electron Shell

The Nucleus

Proton

Neutron

Nucleons

Proton

1

Charge

+

Neutron

1

Charge0

The Electron Shell

Electron

Electron

11836

Charge_

Particle Proton Neutron Electron

Mass1 1 ≈

Charge+1 0 -1

11840

0

Sub-atomic Particles

Charge

+1 0 -1

(+1) + 0 + (-1) = 0

Hence, the total charge of the atom is

0.

In other words, the atom is

electrically neutral

3517Cl

Nucleon No.

Proton No.

Symbol

Proton No.

3517Cl

Tells us the no. of protons

Tells us the no. of electrons

17

17

3517

Cl

Nucleon No.

Tells us the no. of protons + neutrons

No. of neutrons = Nucleon no. – Proton no. = 35 – 17

= 18

Let’s assess…

Find the number of sub-

atomic particles of the

elements given.

Elements

Protons Neutrons

Electrons

Sodium

Calcium

BeryliumHydrogenChlorine

Bromine

Elements

Protons Neutrons

Electrons

Sodium 11 12 11

Calcium 20 20 20

Berylium

4 5 4

Hydrogen

1 0 1

Chlorine 17 18.5 17

Bromine 35 45 35

Isotopes

Chlorine has an atomic mass of 35.5

-Due to isotopes

What are isotopes?

Isotopes

Atoms of the same element with the same number of protons but

different number of neutrons.

Isotopes

Same chemical properties but slightly

different physical properties.

Why?

Isotopes

Chemical reactions only involve electrons.

Physical properties depend on the atomic mass.

As isotopes only differ in atomic

mass but not proton no., they will have

slightly different physical

properties.

Isotopes

Uses?

Some isotopes emit high-energy radiation.

Radiation can damage living cells but can be useful if used wisely.

Radioisotopes

How are electrons arranged?

Electrons are in orbit around the nucleus… Sort of like the planets around the Sun

Why must we know how electrons are arranged?

Electron arrangement determines the chemical properties of the atom.

To ensure that the electron path is smooth

sailing, the electrons are ‘assigned’ levels.

The first level only takes in 2

electrons. Subsequent levels can

only take up to 8 electrons.

Hence, once the level is filled up, the

electrons will ‘create’ another level up

to orbit in.

The way the electrons are arranged is

called an electronic

structure.

2.

1st Shell

2nd Shell

3rd Shell

8. 8

1)Write an electronic structure of sodium atom

2) Draw its atomic structure

2.8.1

11 p12 n

Valence Electrons

Valence = Outermost

Valence shell = Outermost shell

Valence electrons

Electrons on the outermost shell.

Valence Electrons

Chemical property of an element depends on the valence electrons.

Elements with the same number of valence electrons have similar chemical properties.

All atoms yearn for a full outermost shell.

They will go around

1)gaining or

2)losing electrons

to attain a full electron shell (2 or 8

electrons).

Once they have attained the full shell,

they would have a stable electronic

structure.

Formation of Ions

Gaining of electrons:Outermost shell 6 electronsNeed 2 electrons to be full.Electrons gained 2 electrons

The positive nucleus attracts the negative electrons

No. of proton

s

Charge of

protons

No. of electro

ns

Charge of

electrons

No.of neutron

s

Charge of

neutrons

Overall Charge

8 (+1) x 8= +8

8 (-1) x 8= -8

8 0 x 8 = 0

(+8) + (-8)

= 0

No. of protons

Charge of protons

No. of electrons

Charge of electrons

No.of neutrons

Charge of neutrons

Overall Charge

8 (+1) x 8 = +8

10 (-1) x 10 = -10

8 0 x 8= 0

(+8) + (-

10) = -2

Overall charge

Atom:

Ion:

When electrons are gained, the

overall charge is changed and atom

becomes a negative ion.

They are known as ANIONS

2-[ ] O2-

168

Losing electrons:Outermost shell 2 electronsElectrons lost 2 electrons

Outermost shell disappears, exposing the next full shell.

No. of proton

s

Charge of

protons

No. of electro

ns

Charge of

electrons

No.of neutron

s

Charge of

neutrons

Overall Charge

12 (+1) x 12

= +12

12 (-1) x 12= -12

12 0 x 12 = 0

(+12) + (-12)

= 0

No. of protons

Charge of protons

No. of electrons

Charge of electrons

No.of neutrons

Charge of neutrons

Overall Charge

12 (+1) x 12 = +12

10 (-1) x 10 = -10

12 0 x 12= 0

(+12) + (-

10) = +2

Overall charge

Atom:

Ion:

[ ]

When electrons are given away, the

overall charge is changed and atom

becomes a positive ion.

They are known as CATIONS

2+Mg2+

24

12

Try them yourselves!

Write the electronic

structure and draw the

structure of the ions that will

form from the following atoms.

Na, Ca, Cl, O, N, F, K