chemistry chapter 1

elemets key facts 

-when two or more elements join together a molecule is formed 

-compounds contain two or more elements chemically combined 

-mixtures contain two or more substances that are not combined 

The plum pudding modle was the first nuclear model developed by J.J thompson it concluded that every atom has a sphere of positive charge with electrons dotted around it with no nucleas. 

The final structure of the nuclear model was developed by Rutherford due to the alpha scattering experiement and concluded that every atom had a nucleas containing protons and neutrons with energy levels arranged around it containing electrons, because the number of protons and electrons was the same it was discovered that atoms have no overall charge. 

The top number of an element is always the mass number as it equals the number of protons and neutrons the bottom number is the atomic number which is the number of protons and the number of electrons as these are always the same as atoms have no overal charge. 

Ions- atoms can lose or gain electrons without the number off protons in the nucleas changing 

an atom will gain a negative ion if it gains an electron and a positive ion if it loses an electron to gain a full outer shell 

metals will always lose an electron and non metals will always gain one 

- The first shell has a max of 2 electrons 

- The secound shell has a max of 8 electrons 

-The final shell has to have 8 electrons

The number of shells depends on which the group the element is in vertically of the periodic table so if an element is in group 3 it will have three shells 

The sideways groups show how many electrons are in the outer shell of each element 

Metals    

- good conductor of heat  

-lustrous (shiny)

-high density

- can conduct electricity 

-malleable 

solid at 20 degrees 

non metals 

- weak 

- poor conductor of electricity 

- makes a dull sound

- dull appearance

- can be solid liquid or gas at room temperature

-low density 

Reactivity increases as you go down a group this is because the atoms get bigger which means means that the outer electrons are less attracted to the positive nucleas, meaning it is easier to lose the outer electrons 

in a reaction an element may be replaced by a more reactive element