1. A solid substance (ice) melts when heated.

The molecules gain energy & move apart.

T he intermolecular spaces increase & the intermolecular forces weaken, ice becomes water.

2. A liquid (water) evaporates when heated.

The energy of the molecules increases by heating the spaces between them increase & they overcome the intermolecular forces. And some of them escaped as vapour

Melting is the change of solid substance into liquid substance.

Vaporization is the change of liquid into gas.

A molecule consists of atoms.

I f the atoms in the molecule are similar , this substance is an element. An element is the simplest form of a substance.

A compound results from the combination of 2 or more different elements.

Gaseous elements	A molecule consists of 1 atom	Inert gases (noble gases)	Helium, xenon , neon argon, krypton, radon
	A molecule consists of 2 atoms		Oxygen Chlorine Fluorine Hydrogen Nitrogen
Liquid elements		Bromine
	A molecule consists of one atom	Mercury
Solid elements		Magnesium ,aluminium, iron & carbon
Points of comparison	Structure of the molecule	Examples

1. Explain why:

1. The table salt dissolved in water disappears.

………………………………………………………………………………………………………………………………………………………………………………………………………………

2. The volume of a mixture of water & alcohol is less than the sum of their volumes before being mixed.

………………………………………………………………………………………………………………………………………………………………………………………………………………

3. The smell of perfume spreads in the room.

……………………………………………………………………………………………………………………………………………………………………………………………………………………

2. Write the scientific term:

The simplest form of matter that couldn’t be analyzed.
The substance that consists of combination of different elements.
The spaces among molecules.
The smallest part of matter that can exist freely.

3. Match the figure with the following molecules:

1. Hydrogen molecule 2. Water molecule 3. Helium molecule

4 . Sodium molecule 5. Ammonia molecule 6. Iron molecule

4. Match the figure with the process:

1. Figure………………………………..indicates the vaporization process.

2. Figure……………………………….indicates the melting process.

1. Chemists use symbols to express elements.

2. Some symbols come from the Italian name of the element (Latin is an old European language).

3. The symbol is a capital letter, if the symbol consists of 2 letters only the first one is a capital letter.

Element	Atom symbol	Element	Atom symbol
Lithium	Li	Hydrogen	H
Potassium	K	Oxygen	O
Sodium	Na	Nitrogen	N
Calcium	Ca	Fluorine	F
Magnesium	Mg	Chlorine	Cl
Aluminium	Al	Bromine	Br
Zinc	Zn	Iodine	I
Iron	Fe	Helium	He
Lead	Pb	Argon	Ar
Copper	Cu	Sulphur	S
Mercury	Hg	Phosphorous	P
Silver	Ag	Carbon	C
Gold	Au	Silicon	Si

S cientists found that atoms consist

of a nucleus & electrons.

The nucleus	The electrons
The central core of the atom. Consists of protons & neutrons. Carries positive charges. It has most of the mass of the atom.	They revolve in orbits around the nucleus Their charge is negative Their masses are small (negligible)

Protons	Neutron
Positively charged	1. Neutral (carry no charge)
Exist in the nucleus	2. Exist in the nucleus
The mass of a proton almost equals that of a neutron, together protons & neutrons contain most of the mass of the atom.

The number of protons in the atom of an element is unique & characterizes the element.

The atomic number is the number of protons in an atom.

The mass number is the sum of protons & neutrons in an atom.

Atomic number (written at the left side below the symbol is 8) = 8 protons.

Mass number (written at the left side above the symbol is 16)

No. of neutrons = 16 – 8 = 8

Nitrogen

Atomic number = no. of protons = 7

Mass number = protons + neutrons = 14

Number of neutrons = 14 - 7 = 7

Complete the following table:

Element symbol	Atomic number	Mass number	Number of protons	Number of neutrons

An atom is electrically neutral because the number of protons = the number of electrons. The positive charge of the proton is opposite to that of the electrons.

Electrons revolve around the nucleus in orbits called energy levels.

1. E nergy levels are places around the nucleus where electrons exist.

2. There are 7 energy levels represented from the nearest to the nucleus to the farthest by the letters K, L, M, N, O , P, Q .

3. The energy of the level increases by the increase of the distance from the nucleus.

4. Each level is saturated (completely filled) with a certain number of electrons.

5. The number of electros which saturate energy levels 1-4 is calculated by the rule 2n²

Where n is the number of the energy level.

No. of energy level	It symbol	The number of electrons that saturate the levels
1	K	2 (1)2 = 2
2	L	2 (2)2 = 8
3	M	2 (3)2 = 18
4	N	2 (4)2 = 32
5	O	32 electrons. The equation isn’t applied because a number of electrons larger than 32 makes the atom unstable.
6	P
7	Q

6. W hen an electron gains a quantum of energy, it moves to a higher energy level. The atom is excited by gaining energy.

7. The excited atom loses the quantum of energy & electrons return to the original level (ground state)

Distributing electrons in energy levels electronic configuration.

Mass number symbol atomic	Electronic configuration
	K 1
	K 1
	K L 1 2
	K L 5 2

Complete the following table:

Symbol

Mass number Atomic number	Electronic configuration

The atom is the basic unit of matter which goes into in a chemical reaction

1. Substances react together producing new substances. The activity which changes the substance into a new material is called chemical reaction.

2. An atom is the unit of the substance which undergoes a chemical reaction.

3. An atom that has less than 8 electrons in the last energy level is active.

It reacts with atoms of other elements to complete the last energy level with 8 electrons. An example: sodium atoms are active because each has an electron in the last energy level. In a chemical reaction sodium gives this electrons to atoms of another element & end up with 8 electrons in the last energy level.

4. I nert gases such as Argon ₁₈Ar has 8 electrons in the last energy level. They are stable & don’t react with other substances.