Chemical Combination Unit -1

Lesson -1

Made By Dr. Niveen Fawzy

The atom & the ion

Element• Is composed of

Molecules• Each

molecule consists of

Atoms

The no. of well known elements are 116 elementsThe atom is electrically neutral in ordinary state because no. of positive protons are equal to the no. of negative electrons

Classification of elementsElements are classified according to their

properties & electronic structure into:

1-Metals

2-Non-metals

3-Noble gases

First : Noble (inert) Gases

• They are elements in which the outermost electron shells are completely filled with electrons , so they don’t participate in any chemical combination in ordinary conditions

• They are monoatomic • They don’t form positive or negative ions in ordinary

conditions

Examples of noble gasesAtom of inert gas

No. of electrons

No. of protons

No. of neutrons

Electron configuration

2 2 2

10 10 10

18 18 22

2P2n

10p10n

18P22n

K

2

K L

2 8

K L M

2 8 8

Nobel gases

Second: Metals & non-metals

Physical properties of both

Chemical properties of both Metals Non-metals

They are elements which have less than (4) electrons in the outermost energy level

They are elements which have more than (4) electrons in the outermost energy level

During chemical reactions metals lose (give) their outermost electrons to other atoms & change to (+) ion

During chemical reactions non-metals gain electrons from other atoms to complete the outermost energy level & change to (-) ion

Mercury is the only liquid metal, while Bromine is the only liquid non-metal

ComparisonsPoints of comparison

Atom Ion

Electrically: Neutral Charged (-) or (+)

No. of electrons: Equal to the no. of protons

More or less than no. of protons

Examples of metals

Examples of metals

Examples of metals

Give reason:• When the atom loses an electron or more during chemical

reaction, it changes into positive ion • Because the no. of electrons becomes less than the no. of

protons• What is an ion?• Its an atom which loses or gains an electron or more during

chemical reactions• What is a positive ion?• Its an atom that loses one or more electrons during the

chemical reaction & carries a no. of positive charges equal to the no. of given electrons

Examples of non-metals

Examples of non-metals

Examples of non-metals

Nitrogen atom (N)

Nitrogen ion (

Give reason:• When the atom gains an electron or more during

chemical reactions , it changes into a negative ion• Because the no. of electrons becomes more than the no.

of protons • What is a negative ion?• It’s the atom which gains an electron or more during the

chemical reaction & carries a no. of negative charges equal to the no. of gained electrons

• N.B Hydrogen is a gaseous non-metal element although it has only one electron in the outermost level (K)

ComparisonPositive ion (cation) Negative ion (anion)

A metal atom that loses an electron or more during chemical reaction

A non-metal atom that gains an electron or more during chemical reaction

It carries positive charges equal to the no. of lost electrons

It carries negative charges equal to the no. of gained electrons

No. of electrons is less than no. of protons

No. of electrons is more than no. of protons

No. of its energy levels is less than that of its atom

No. of its energy levels is equal to that of its atom

Try to think:• What happens to the atomic diameter of an atom when

it loses or gains an electron or more?• When an atom loses an electron or more its diameter &

volume decrease due to lackness of electrons, & attraction of nucleus to remaining electrons increase , so a positive ion diameter is smaller than its atomic diameter

• When an atom gains an electron or more its diameter & volume increase due to increase in the no. of electrons ,& repelling increase between electrons , a negative ion diameter is bigger than its atomic diameter

Chemical bonds

• Atoms combine together to form molecules through chemical bonds

• We will study 2 types of bonds:1- Ionic bond2- Covalent bond

First: Ionic bond• It’s a type of chemical bond that occurs between a metal

atom & a non-metal atom resulting from electric attraction between a (+) &(-) ion

• Steps of formation of ionic bond:1- Metal atom loses electron(s) & changes into a (+) ion2- Non-metal atom gains electron(s) lost from metal atom & changes into (-) ion3- A strong electrical (electrostatic) attraction between (+) & (-) ions occur through ionic bond

Examples of ionic bonds1- Formation of table salt

2-Formation of Magnesium oxideFirst step :

Second step:

Third step:

Its a bond occurred among atoms of non-metals through the participation of each atom with the same no. of electrons to complete the outer electron shell of each atomSteps of formation of covalent bonds:1- Two non-metal atoms interact together , no one loses or gains any electrons2- Each atom shares the other with a no. of electrons equal to the no. needed to complete its outer shell3- An interference occurred among both atoms resulting in covalent bond

Second : Covalent bond

Types of covalent bond• There are 3 types of covalent bonds:• 1- Single covalent bond• 2- Double covalent bond • 3- Triple covalent bond First: Single covalent bond• Its bond arises between 2 non-metals sharing each other

with one electron• Represented by one line joining the two atoms { }

Examples of single covalent bond• 1-Hydrogen molecule

Each hydrogen atom shares with one electron to complete (K) level & become more stable

Single covalent bond 2- Water molecule •

The oxygen atom shares each hydrogen atom with one electron , to complete the outermost shell of all 3 atoms

Single covalent bond• 3- Hydrogen chloride molecule:• The hydrogen & chlorine atoms each share each other

with one electron

Double covalent bond Oxygen molecule

Each oxygen atom shares the other with 2 electrons to complete the outermost shell (L) with 8 electrons & become more stable

The double covalent bond arises between 2 non-metal atoms sharing each other with 2 electrons & is represented by (=) joining 2 atoms

Triple covalent bond Triple covalent bond arises between 2 non-metal atoms sharing each other with 3 electrons to complete the outermost shell & become more stable & is represented by 3 lines Nitrogen molecule

Comparison Ionic bond Covalent bond

Formed by losing or gaining of electrons Formed by sharing one pair of electrons or more

Arises between metal & non-metal elements

Arises between 2 non-metal elements

Formed between 2 atoms of 2 different elements

May be formed between 2 elements of same element

Formed due to electrical attraction between (+) &(-) ions

Formed due to sharing of electrons between atoms

Its only one type Three types : single , double , triple

Produces compound molecules only Produces element & compound molecules

Enrichment information• The Egyptian scientist Ahmed Zweil has been granted

Nobel prize in chemistry in 1999 due to inventing new brands of camera working via laser technologies

Model answers of book lesson 1-unit1• Question (1) (A):• 1- Metal atom 2- Ionic bond 3-Non-metal atom• 4- Triple covalent bond 5- Noble (inert) element• 6- Metals 7- Non-metals• Question (1) (B):• Because iron is a metal element which is malleable so it

will not break, while coal is a non-metal which is not malleable , breaks easily

Model answers of book lesson 1

Atom Electron configurationK L M N

Molecule Type of bond

2 8 1 -

2 8 7 -

NaCl Ionic bond

2 5 - - Triple covalent

Question (2) (A):

Model answers of lesson 1• Question (2) (B):

Model answers of lesson 1• Question (3) (A):

Element Electron configurationK L M N

Its type Its ion

2 8 6 - Non-metal

2 8 2 - metal

2 8 8 - inert gas no ion

Model answers of lesson 1• Question (b) Give reason:• 1- Because sodium (metal) atom joins with chlorine (non-

metal) atom by transferring one electron from Na to Cl & ionic compound is formed . While chlorine atom joins with other chlorine atom by sharing with one electron for each atom to form covalent molecule.

• 2- Because the no. of electrons becomes less than no. of protons

• 3- Because the no. of electrons becomes more than the no. of protons

Model answers of lesson 1• 4- Because ionic bond arises between 2 different atoms

(metal & non-metal) , while covalent bond arises between 2 similar or different non-metal atoms

• 5- Because each oxygen atom shares with 2 electrons to form double covalent bond

• 6- Because magnesium loses 2 electrons & change into (+) ion , while oxygen gains the 2 electrons lost by (Mg) & changes into (-) ion , then electric attraction occurs between both ions

Model answers of lesson 1• Question (4): comparison:• Refer to previous slides for comparison tables• Question (5):• What is a positive ion?• Its an atom that loses one or more electrons during the chemical reaction

& carries a no. of positive charges equal to the no. of given electrons• What is a negative ion?• It’s the atom which gains an electron or more during the chemical reaction

& carries a no. of negative charges equal to the no. of gained electrons• What is an ion?• Its an atom which loses or gains an electron or more during chemical

reactions