Can you recall…

What is Matter?

Matter is anything that has mass and takes up space.

Can you recall…

What is the kinetic particle theory?

Can you recall…

What is the kinetic particle theory?

The Kinetic Particle Theory states that matter is made of tiny discrete particles (atoms or molecules), which are in constant and random motion.

So, what is an atom?

solidliquidgas

Atom!Atom!

So, what is an atom?

An atom is the smallest unit of an element, having the properties of that element.

Do you think a copper atom is identical to a zinc atom?

Are atoms like solid balls?

With nothing else inside?

Subatomic Particles

Atoms - made up of subatomic particles

electron

proton

neutronnucleus

positively charged

neutral

negatively charged

Note: The nucleus consists of protons and neutrons

Subatomic Particles

Particle Symbol Relative Mass

Charge

Proton p 1 1+

Neutron n 1 0

Electron e- 1/1836 1-

electron

proton

neutronnucleus

positively charged

neutral

negatively charged

Thinking Time…

Why is the term "relative mass" used rather than just mass?

Particle Symbol Relative Mass

Charge

Proton p 1 1+

Neutron n 1 0

Electron e- 1/1836 1-

Thinking Time…

Hints…

Mass of proton = ~1.67×10−27 kg

Mass of neutron = ~1.67×10−27 kg

Mass of electron = ~ 9.11×10−31 kg

Thinking Time…

Mass of proton, neutron and electron are too small and inconvenient to work with.

By using relative mass, we do not have to remember the exact value of the various masses.

Counting protons…

Proton Number

The number of protons in an atom is called the proton number. Proton number is also known as the Atomic Number.

Counting protons & neutrons…

Nucleon Number

Nucleon number is the number of protons and neutrons in the nucleus of an atom. Nucleon number is also called the Mass Number.

Nucleon Number

Nucleon (Mass) number =

number of protons + number of neutrons

• Carbon atom in symbol form: C.

• Can also be written as carbon-12.

12

6

Question

How many protons, electrons, and neutrons are there in a C atom?

6 protons, 6 electrons and 6 neutrons.

12

6

Worksheet Time…

• Try Question 1 to 4

The Atomic Model

The centre of an atom is called the nucleus which contains the protons and neutrons.

protons

neutronsnucleus

The Atomic Model

The electrons in an atom are arranged in shells (orbits) at different distances from the nucleus.

Note: Shells are also called energy levels.

protons

neutronsnucleus

1st shell 2nd shell 3rd shell 4th shell

electron

The Atomic Model

1st shell

2nd shell3rd shell

4th shell

electron

Each shell can hold a certain maximum number of electrons.

Advanced: For elements after calcium in the 4th period, their third shell can hold up to 18 electrons.

(a) 1st shell - 2 electrons

(b) 2nd shell - 8 electrons

(c) 3rd shell - 8 electrons (1st 20 elements only)

Question

An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus.

Question

An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus.

(a) Why is the atom electrically neutral?

Number of electrons = number of protons. Equal positive and negative charges

(b) Why is the nucleus positively charged?

The nucleus contains protons and neutrons. Protons are positively charged while neutrons are electrically neutral.

Differentiating different elements

How do I differentiate the atoms of one element from the atoms of another element?

All atoms of the same element have the same number of protons while those of different elements contain different number of protons.

12

6C

23

11Navs

Worksheet Time…

• Try Question 5

Advanced: Isotopes

• Isotopes are atoms of the same element with different numbers of neutrons.

-> same proton number, different nucleon number

• E.g. carbon has 3 isotopes:12

6C

13

6C

14

6C

Electron Arrangement

• Nitrogen-14 atom has 7 electrons

7 p

7 n

Key• - electronp - protonn - neutron

Drawing the full electronic configuration

Note: full electronic configuration of an atom shows the arrangement of electrons in different shells.

Electron Arrangement

• Nitrogen-14 atom has 7 electrons

7 p

7 n

Key• - electronp - protonn - neutron

Writing the electronic configuration: 2.5

shows arrangement of electrons in different shells.

1st shell2nd shell

separate the 2 shells

Electron Arrangement

• Argon-40 atom has 18 electrons

18 p

22 n

Key• - electronp - protonn - neutron

electronic configuration of 2.8.8

Valence Shell

• Valence shell - farthest occupied shell from the nucleus

• Valence electron - electron in the valence shell

7 p

7 n

Valence Shell

• Note: only valence electrons are involved in chemical reactions.

7 p

7 n

Outer electronic structure

• only valence electrons are drawn

7 p

7 n

Key• - electronp - protonn - neutron

Thinking Time…

Based on what you have learnt in this topic, describe how are the elements in the Periodic Table being arranged?

Arrangement of elements in the order of increasing proton (atomic) number.

Formation of Ions

• During chemical reactions, some atoms might lose/gain electron(s). Atom becomes an ion (charged particle) when it gains or loses electron(s).

Question

Why does an atom become a charged particle when it gains or loses electron(s)?

An atom is electrically neutral because number of electrons = number of protons (equal positive and negative charges).

When it gains or loses electron(s), the positive and negative charges are not balanced. Therefore, the atom becomes a charged particle.

Formation of cations

• When an atom loses one or more electrons, it becomes a positively charged particle called cation.

Lithium atom (Li)3 electrons3 protons

Net charge: 0

Lithium ion (Li+)2 electrons3 protons

Net charge: +1

Formation of anions

• When an atom gains one or more electrons, it becomes a negatively charged particle called anion.

Fluorine atom (F)9 electrons9 protons

Net charge: 0

Fluoride ion (F-)10 electrons

9 protonsNet charge: -1

Question for Thought

Why do atoms become ions?

To obtain a full valence shell

To obtain the same electronic structure of a noble gas so as to be stable. (Note: this will be covered under chemical bonding)

Worksheet Time…

• Try Question 6 to 8

Exercise Charge of ion Element Name of ion Symbol of ion No. of electron gained No. of electron lost

-2 OxygenSulfur

OxideSulfide

O2-

S2- 2

-1 FluorineChlorine

FluorideChloride

F-

Cl- 1

+1 HydrogenLithiumSodium

Potassium

HydrogenLithiumSodium

Potassium

H+

Li+

Na+

K+

1

+2 BerylliumMagnesium

CalciumCopper

Iron

BerylliumMagnesium

CalciumCopper (II)

Iron (II)

Be2+

Mg2+

Ca2+

Cu2+

Fe2+

2

+3 AluminiumIron

AluminiumIron (III)

Al3+

Fe3+ 3

Exercise

Do metals generally form cations or anions?

cations

Do non-metals generally form cations or anions?

anions