chemistry sem 1

Atomic number

number of protons OR number of electrons

Mass number

number of protons + number of neutrons

Isotopes

are atoms of the same element with different numbers of neutrons

Cation

formed when an atom loses an electron ( positive ion)

Anion

formed when an atom gains an electron (negative ion

What is an ion

is a charged particle that contains an unequal number of protons and electrons

Emission spectra and electron shells

Ø When atoms are heated in a flame, the electrons gain energy and become excited. With this extra energy, they can jump from their normal shell to the next outer shell. When they return to their original shell, the energy is lost in the form of light

– the alkali metals

they are soft ( softness increases across the group) , have low density, have low melting and boiling points, good conductors of heat and electricity, they are shiny

alkali earth metals

highly reactive (but not as reactive as alkali metals), silver colour, more dense and harder than the alkali metals  

Transition metals

Shiny, good conductors, high Melting Point,very malleable and ductile

noble gases

colourless,  low chemical reactivity  , low melting and boiling points

Electronegativity

increases across a period, decreases down a group

group 1 and 2 reactivity

Groups 1 and 2 reactivity increases downwards

group 16 and 17 reactivity

reactivity increases upwards

metals reactivity

increases as you move down a group (column) and to the left across a period (row) on the periodic table

non metals reactivity

increases across a period, decreases down a group

what are Metalloids

elements which have both metallic and non-metallic   characteristics/properties

Allotropes

are different physical forms of the same elements

Metals properties

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

Non metals properties

usually dull, poor conductors of heat and electricity, brittle, can be solids, liquids or gases at room temperature

Electrostatic attraction

the attraction between protons and electrons

Ionic bonding

– occurs between metal atoms and non-metal atoms

Covalent bonding

- occurs between non-metal atoms

Metallic bonding

occurs between metal atoms  

Properties of ionic compounds

± Are solid at room temperature, are brittle and hard, high melting and boiling points

Metallic bonds structure

± In metals, the atoms are packed tightly together in a regular pattern, which allows outer electrons to separate from their atoms which results in a lattice of ions in a sea of electrons

What holds the atoms together

the electrostatic attraction between the network of cations and the delocalised valence electrons

Why are metals good conductors of electricity

because of their freely moving ‘cloud’ of delocalised electrons can move easily through the metal’s structure

Why do metals have high melting and boiling points

because the forces between the network of positive ions and the free moving electrons are strong

Why are metals ductile and malleable

When a metallic structure is struck with force, the lattice's cations are pushed closer together, while delocalized electrons move, maintaining the attraction between the cations and electrons.

Why are metals lustre

because the freeing moving electrons are able to reflect light.

Metal alloy

is a mixture of two or more metals.

Alloys are harder than pure metals because the atoms are of different sizes and therefore do not consist of layers which can slide over each other

Memory alloy

alloys that can return to their original shape if damaged

The law of conversion of mass

The mass of the products after a chemical reaction is equal to the mass of the reactants before the reaction.

(States that -mass cannot be created or destroyed in a chemical reaction

halogens

highly reactive and toxic

what do you need to form a ionic compound

a anion and cation

polyatomic ions

an ion that is composed of two or more atoms covalently bonded

hydrogen bonding

occurs between the nitrogen bases