Chemistry c4 c5 c6

Structure of an atom

- nucleus is made up of protons and neutrons

- space around the nucleus is occupied by negativley charged electrons in shells.

Elements and compounds

- element is a substance that cannot be broken down chemically

- compound is a substance which contains at least two elements that are chemically combined

-e.g. Sodium chloride contains the elements sodium and chlorine

Atomic number

- Arranged in order of ascending atomic number, It is the number of protons in the atom

Isotopes

- different number of neutrons

- Have the same atomic number but different mass number, mass number is the number of protons and neutrons

- Tells us how many electrons are arranged around the nucleus

-e.g. Aluminum has the electronic structure 2.8.3 this means it has 3 occupied shells and a total of 13 electrons

- atoms are not charged

- However an ion is a charged atom or group of atoms e.g. Na+ 

- Positive ion is formed when an atom or atoms lose one or more electrons

ATOM OR GROUP -- ELECTRONS = POSITIVE ION

- Negative ion is formed when an atom or atoms gains one or more electrons

ATOM OR GROUP + ELECTRONS = NEGATIVE ION

- Atoms form ions to gain a full outer shell

- Metal and non metal combine by transferring electrons, Metal atoms transfer electrons to become postitive ions and non metals recieve electrons to become negative ions

- The ions are then attracted to each other as they are negatively charged.

- Arranged in order of ascending atomic number

- vertical column in the table is a group, they have similar chemical properties, they all have the same number of electrons in their outer shell e.g. group 1 elements have 1 electron in the outer shell

- Horizontal row of elements is called a period. it corresponds with the number of shells of electrons e.g. elements in period 3 have 3 shells of electrons

- Covalent bonding is where non metals combine by sharing electrons

- Ionic bonding is where metals and non metals combine by sharing electrons

- they are alkali metals and need to be stored under oil as they react highly with water

- lithium gives off a red flame, sodium gives off a yellow and potassium gives off a lilac flame

- Alkali metals react with water to produce hydrogen and hydroxide, they react more highly as you go down the group

-LITHIUM + WATER = LITHIUM + HYDROGEN

2LI + 2H20 = 2LIOH + H2       etc

- Halogens - non metals

- Flourine, Chlorine, Bromine, iodine

- Chlorine is a green gas, Bromine is an orange liquid and iodine is a grey solid

- They react highly with alkali metals to form metal halides e.g. Lithium + Chlorine = lithium chloride

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