Atomic Structure And The Periodic Table 2

Chemistry

Unit 2 Sheet 4

PreIGCSE

Atomic structure and the Periodic table

Key ideas ➢

➢

The atomic mass is determined by the weight of the protons and neutrons, as the mass of electrons is negligible as shown in the following table: Particles

Relative Mass

Relative Charge

Proton (p)

1

+1

Electron (e)

1/1840

Neutron (n)

1

-1 0

The unit of measurement of the mass of the atom is the atomic mass unit and its symbol is AMU and it equals the mass of one proton

proton

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Chemistry

Unit 2 Sheet 4

PreIGCSE

s the relative atomic mass in AMU it equals the sum of protons and neutrons , it is the sam

umber of protons + number of neutrons

ngement of elements in the periodic table : periodic trends

➢

In the periodic table , the elements are arranged in order of proton number. Elements with similar chemical properties are placed in the same group

➢ Elements in a group have the same Chemical properties Outer electron distribution Valency in most cases ➢

Moving across a period (from left to right) the elements change from metallic to non-metallic. The number of valency electrons increases across the period but the number of occupied energy levels stay the same

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Chemistry

Unit 2 Sheet 4

PreIGCSE

➢ The periodic table is divided into 3 areas; metals, nonmetals and metalloids

Chemical differences between metals and nonmetals: Chemical Property

Electronic distribution bonding

Type compound

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Metals

Non-Metals

– 1, 2 or valency electrons. and

–

3

– 4, 5 ,6 or 7 valency electrons. –

Either gain electrons to form anions (negative anions) or share electron pairs.

–

Form ionic compounds with metals

These are lost to form cations (positive ions)

of Form compounds non-metals

ionic with

Chemistry

Unit 2 Sheet 4

–

Class of oxide

Reaction acids

PreIGCSE

Metal oxides are usually basics, a few are amphoteric

–

Form covalent compounds with other non-metals

–

Non-metal oxides are usually acidic; a few are neutral

Many react with with dilute acids to give Do not react with a salt and dilute acids hydrogen

Physical differences between metals and nonmetals Metals

Non-metals

Usually have high melting and boiling points Exceptions: Group 1 metals have low melting points and mercury is a liquid

Melting points and boiling points are low Exceptions: those non-metals with macromolecular structures – carbon, silicon, boron , germanium

Good conductors of both heat and electricity

Poor conductors Exception: graphite

Hard Exceptions: Group 1 metals are soft

Soft Exceptions: those non-metals with macromolecular

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Chemistry

Unit 2 Sheet 4

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structures- carbon , boron, silicon, germanium High densities Exceptions: Group 1 metals have low densities

Low densities

Malleable (can have their shape changed by hammering)and Ductile (can be pulled into wires)

Brittle Exception: graphite

Sonorous (think of a bell)

Not sonorous

Shiny ( can be polished to a lustre)

Have a dull surface Exception: graphite, iodine

Exercise 2-1: 1- Calcium and phosphorus are in the same period in the periodic table . a- Which one will be the better conductor of electricity ? Give a reason for your choice ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------b- Complete the following word equations. If the substances do not react, write “no reactions” Calcium + hydrochloric ----------------------------------------------

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acid

→

Chemistry

Unit 2 Sheet 4

Phosphorus + hydrochloric →-------------------------------------------1-

PreIGCSE

acid

Selenium is a non-metal in Group VI a- Predict three physical properties of selenium ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------b- How many valency electrons are there in one selenium atom ? ----------------------------------------------------------------------------------------------

1- Germanium is a non-metal in Group IV a- Complete the electronic distribution of a germanium atom. Two numbers are missing ------, 8 , 18 , ------b- Carbon and Germanium are both non-metals. They are both poor conductors of electricity. Predict which is the better conductor, giving a reason for your choice ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

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Chemistry

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Unit 2 Sheet 4

PreIGCSE