IGCSE Chemistry

Examples of mixtures

water and iron filings, salt and sand, pepper and water

3 groups of elements

metals, metalloids, non-metals

Properties of metals

good conductors of heat and electricity, malleable, ductile, shiny, solid at room temperature

Examples of metals

Gold, copper, aluminum

Properties of non-metals

poor conductors of heat and electricity, not ductile or malleable, dull, brittle, mostly gases

Examples of non-metals

oxygen, carbon, chlorine

Atom

The smallest particle of an element

Element

A pure substance made of only one kind of atom and cannot be broken down into simpler substances

Examples of elements

Hydrogen, Helium, Lithium

Compound

A substance made up of atoms of two or more different elements chemically combined together and can be separated by chemical means

Examples of compounds

water, carbon dioxide, sucrose

Mixture

A combination of two or more substances that are not chemically combined and can be separated by physical means

Properties of metalloids

They have properties of both metals and nonmetals

Examples of metalloids

germanium, silicon, arsenic

Alloy

A mixture of two or more metals

Properties of alloys

They are usually stronger than metals

Why alloys are harder than pure metals

The regular layers in pure metal are distorted by atoms of different sizes in an alloy

Examples of alloys

Brass = Copper + Zinc

Bronze = Copper + Tin

Steel = Iron + Carbon

Transition metals

Elements that form a bridge between elements on the left and right sides of the periodic table

Properties of transition metals

Good conductors of heat and electricity

Examples of transition metals

gold, silver, copper

Nucleus

The dense, positively charged center of an atom made up of protons and neutrons

Particles of an atom

protons, neutrons, electrons

Mass of particles in an atom

electron--almost 0; proton--1; neutron--1

Charges of particles in an atom

electron--negative; proton--positive; neutron--neutral

Atomic number

The number of protons in an atom, also known as proton number

Mass number

The total number of protons and neutrons in the nucleus of an atom

Mass number formula

protons + neutrons

Relative atomic mass

A weighted average of the masses of the atoms of the isotopes and takes account of the abundance of each of the isotopes of the element

Relative atomic mass vs mass number

Mass numbers are always whole numbers while relative atomic masses are usually rounded off to the nearest whole number, but are not whole numbers

Number of neutrons formula

mass number - atomic number

Number of electrons

=number of protons

Isotope

An atom with the same number of protons and a different number of neutrons from other atoms of the same element.

Properties of isotopes

Same chemical properties, different physical properties (e.g. boiling/melting point)

Examples of isotopes

Carbon-12, Carbon-13, Carbon-14

Periodic table

A table that shows the elements, their atomic number, symbol, and average atomic mass; elements with similar chemical properties are grouped together.

Shell

An area in an atom, around its nucleus, where electrons are found

Period

A horizontal row of elements in the periodic table; it shows the number of shells an element has

Reactivity of metals along a period

reactivity decreases as you go from left to right across a period

Reactivity of non metals along a period

reactivity increases as you go from left to right across a period

Group

A vertical column of elements in the periodic table; it shows the number of valence electrons an element has

Reactivity of metals down a group

reactivity increases as you go down a group

Reactivity of non metals down a group

reactivity increases as you go up a group

Atomic structure

proton(in nucleus)

neutron(in nucleus)

electron(outside nucleus and in shells)

Ways to represent atomic structure

Electronic configuration, dot and cross diagrams

Electronic configuration

The arrangement of electrons in shells around the nucleus of an atom represented numerically

Example of electronic configuration

Oxygen - (2,6)

Sodium - (2,8,1)

Calcium - (2,8,8,2)

Isoelectronic

When two ions have the same electron configuration

Dot and cross diagram

A drawing to show the arrangement of the outer shell electrons only of the atoms or ions in a substance

Example of a dot-and-cross diagram

Maximum number of electrons in shells

1st shell: 2

2nd shell: 8

3rd shell: 8

Which shells are filled first?

1st shell, 2nd shell, 3rd shell and so on

Note: The previous shell should be completely filled first before drawing another shell

Chemical bonding

The joining of atoms to form new substances

Why elements bond

To become stable and have 8 electrons in their outermost shell

Elements that are stable

Elements in group 8 of the periodic table

Elements that are not stable

Elements from group 1-7 of the periodic table

How elements become stable

They have to either gain or lose electrons

Ion

An atom or group of atoms that has a positive or negative charge.

Charge

A measure of the extra positive or negative particles that an atom or group of atoms has

Cation

A positively charged ion or (has more protons than electrons)

Examples of cations

Sodium (Na+), Potassium (K+), Lithium (Li+)

Anion

a negatively charged ion (has more electrons than protons)

Examples of anions

Chloride (Cl-), Bicarbonate (HCO3-), Sulfate (SO4-)

Types of bonding

ionic, covalent, metallic

Ionic bonding

The electrostatic attraction between positive and negatively charged ions

Ionic bonding occurs between

metals and non-metals

Examples of ionic compounds

NaCl, MgO

Explain in terms of bonding and structure why ionic compounds have high melting points

Ionic compounds have high melting points because a large amount of energy is needed to break the strong ionic bonds in its giant ionic lattice

Why is NaCl not a conductor of electricity in the solid state but is a conductor of electricity in the liquid/aqueous state

NaCl is an ionic compound. In NaCl(aq) and NaCl(l), there are freely moving ions which can carry charges, therefore they are conductors of electricity. In NaCl(s), the ions are not free to move and are tightly packed in its giant ionic lattice. Therefore, they cannot carry charges and conduct electricity.

Covalent bonding

The electrostatic attraction between the positively charged nucleus and the shared pair of electrons

Covalent bonding occurs between

non metal and non metal

Examples of covalent compounds

CO2, H2O

Naming covalent compounds

Add prefixes( mono-1, di-2, tri-3, tetra-4, penta-5, hexa-6, hepta-7, octa-8, nona-9, deca-10) to elements and add -ide to the end of the anion

Explain why CO2 has a low melting and boiling point

The bonding in CO2 is covalent. A small amount of energy is needed to overcome the weak intermolecular forces of attraction in its simple molecular structure, hence it has a low melting and boiling point.

Giant covalent structure

A structure with many atoms joined to each other by lots of strong, covalent bonds giving a high melting point and (except for graphite) poor electrical conductivity.

Examples of giant covalent structures

Diamond, graphite, silicon dioxide

Explain why graphite has a high melting/boiling point

Graphite has a high melting/boiling point because each carbon atom is covalently bonded to 3 other carbon atoms, which in turn, are bonded to 3 more carbon atoms. This forms a continuous layer of hexagons. I is difficult to break these many strong covalent bonds, therefore it has a high melting/boiling point.

Why is graphite soft and slippery?

Graphite is soft and slippery because it is made up of man layers of carbon atoms on top of each other and they are held loosely by weak intermolecular forces of attraction between the layers so the layers can slide on top of each other when a force is applied, making graphite soft and slippery.

Why does graphite conduct electricity?

Graphite conducts electricity because each carbon atom has 1 outer electron that is not used to form covalent bonds. These electrons can move freely along the layers from 1 carbon atom to the next. They are said to be delocalized These free-moving electrons allow graphite to carry charges and conduct electricity.

Metallic bonding

The electrostatic attraction between the positively charged metal ions and the sea of delocalized electrons

Metallic bonding occurs between

metal and metal

Characteristics of metals

Good conductors, solid at room temperature (except mercury), luster, ductile and malleable

Explain in terms of bonding why metals have high melting/boiling points

Metals have high melting/boiling points because a high amount of energy is needed to break its strong metallic bonds in its giant ionic lattice

Chemical reaction

the process by which 1 or more substances change to produce 1 or more different substances

Endothermic reaction

A reaction in which energy is absorbed

Exothermic reaction

A reaction that releases energy in the form of heat

Chemical word equation

uses words to describe the reactants and products(reactant + reactant -> products)

Example of chemical word equation

oxygen + hydrogen -> water

Balanced symbol equation

An equation written in such a way that the number of each type of element is equal on both sides.

Example of balanced symbol equation

2H2 + O2 -> 2H2O

Steps to write a balanced equation

Step 1: Make sure you know what the reactants are

Step 2: Write out the word equation

Step 3: Write out the equation using the formulae of the elements and compounds

Step 4: Balance the equation

Types of chemical reactions

synthesis, decomposition, single replacement, double replacement, combustion

Synthesis

a chemical reaction in which two or more substances combine to form a new compound (A + B --> AB)

Decomposition

a chemical reaction that breaks down compounds into simpler products (AB --> A + B)

Single replacement

a chemical reaction where one element replaces another element in a compound (A + BC --> AC + B)

Double replacement

a chemical reaction where two elements in different compounds trade places (AB + CD --> AD + CB)

Combustion

a chemical reaction between oxygen and fuel that results in carbon dioxide and oxygen

State symbols

They show the state of a substance

(s) solid

(l) liquid

(g) gas

(aq) aqueous

Aqeuous

dissolved in water

Solubility rules

1. Na and K salts are soluble

2. NH4+ salts are soluble

3. NO3- is soluble

4. Ethanoates are soluble

5. So4 2- soluble except CaSO4, BaSO4, PbSO4

6. Cl- soluble except AgCl and PbCl2

7. CO3 2- insoluble except NaCO3, K2CO3, and (NH4)2 CO3