c4 revision

In 1869, Mendeleev presented his periodic table, which is much like the one we use today. Mendeleev left gaps for unknown elements and even predicted their properties.An element is made up of only one kind of atom. All atoms of an element have the number of protons. Elements are arranged in acscending order of proton number, which gies repeating patterns to the propertiesof the elements. 

By using a periodic table you can:

- find the relative atomic mass

- find the symbol

- find the name

- work out the proton and neutron number

A vertical column of elements is called a group; these elements have similar properties. the group number corrrespnds to the number of electrons in the outer shell. A horizontal row of elements is called a period. Period number corresponds to how many shells of electrons an element has. 

An atom has a small, central nucleus, which consists of protons and neutrons, and has electrons arranged in shells around it. If an atom has the same number of protons as electrons, then the atom as a whole is neutral. A proton has the same mass as a neutron, and an electron's mass is so tiny it is regarded as zero.

ATOMIC PARTICLE              RELATIVE MASS                     RELATIVE CHARGE

Proton                                              1                                                +1

Neutron                                            1                                                  0

Electron                                            0                                                 -1

Only two electrons can be held in the first shell. After that only eight electrons can be held by each shell.

NO ATOMS CAN BE LOST OR MADE 

How to protect yourself while doing experiments:

- wear prtotectie gloves/goggles/apron

- washing hands after experiment 

- using safety screens

- using small amounts and low concentrations

- working in a fume cupboard or ventilating the room

- not eating or drinking

- not using flammable substances

Only six. The further you go DOWN the group, the HIGHER the REACTIVITY, the LOWER the melting and boiling points, and the HIGHER the density. 

In group 1, the alkali metals all have similar properties because they all have one electron in their outer shell.

Alkali metals become more reactive the further down the group because the electron in the outer shell is further away from the influence of the nucleus and is therefore lost more easily. 

Alkali metals:

-can react to form compounds. 

- are shiny but quickly tarnish in moist air, become dull and become covered in a layer of metal oxide. 

- react vigorously with chlorine to form white crystalline salts. 

- react with water to form metal hydroxide/ the metal hydroxide dissolves in water to form an alkaline solution.

(where M means alkali metal)

2M(s) + 2H2O(l) -> 2MOH(aq) + H2(g)

(s) solid     (l) liquid     (aq) aqueous solution     (g) gas

When working with alkali metals the following precautions should be in order:

- use small amounts

- wear protection (gloves / goggles /safety screens

- avoiding working near flames

- ensure metals are stored in oil and lids are tightly secured.

The are five non-metals in group 7.

At room temperature and pressure:

- chlorine is a green gas

- bromine is a brown liquid

- iodine is a dark purple/dull grey solid (iodine turns into a purple gas when heated).

All halogens consist of diatomic molecules (they only exist in pairs of atoms).

Halogens can be used to:

- bleach dyes

- kill bacteria 

The FURTHER down the group you travel the LOWER REACTIVITY, the HIGHER the melting and boiling points, and the HIGHER the density. 

Halogens react with alkali metals to produce HALIDES.

(where M means alkali metal and G means halogen)

2M(s) + G2(g) -> 2MG(s)

(s) solid (g) gas

Halogens all have similar properties because they all have SEVEN electrons in their outer shell. Halogens become LESS reactive as you go down the group because the atoms get larger; the outer shell gets further from the nucleus and therefore the electron shells are further away from the influence of the nucleus and so an electron is less easily gained. 

Hazards:

- wear safety glasses                                                                                                               - work in a fume cupboard/ well-ventilated area                                                                         - use small amounts of very dilute solutions                                                                             -- avoid working near naked flames                                                                                           - watch teacher demonstrations very carefully

A more reactive halogen will displace and less reactive halogen. Halogens react with other elements to form compounds- highly exothermic- form ionic compounds. 

properties of compounds made from halogens and alkali metals:

- conduct electricity when molten or dissolved in water

- made up of charged particles called ions.

Ions are atoms that have gained or lost electrons. 

as the number of protons and electrons are o longer equal, ions have an overall charge. 

Atoms that have gained electrons have a negative charge.

Atoms that have lost electrons have a positive charge.

Ionic bonding:

- occurs between metals and non-metals

- form salts (ionic compounds)

Ionic compounds form crystals because the ions are arranged in a regular lattice. when ionic crystals melt or are dissolved in water they conduct electricity; the charged ions are free to move around.  

Ionic compounds are electrically neutral substances that have equal amounts of positive and negative charge.