Chemistry Unit 1 Key Notes on all topics

All elements are made up of atoms. When two or more atoms join together a molecule is formed. The atoms in elements and compounds are held tightly to each other by chemical bonds.

When two elements are mixed together we can often separate them again quite easily because the molecules in the elements are not joined together by chemical bonds like in compounds. Instead they are mixed together but are separate from each other instead of being tightly packed together.

The three particles that make up an atom are protons, neutrons and electrons. An oxygen atom has 8 protons so it also has 8 electrons.

The fourteenth element on the periodic table is Silicone.

In the nucleus of atoms there are protons and neutrons. Around the nucleus there are electrons which have a negative charge. In the periodic table, atoms are arranged in order of their atomic number.

Atoms are always neutral because the number of protons which have a positive charge is always equal to the number of electrons which have a negative charge. Neutrons are neutral so do not have a charge. This results in no overall charge of atoms.

A nitrogen atom whose atomic number is 7 and mass number is 14 has 7 protons, 7 electrons and 7 neutrons.

A chlorine atom whose atomic number is 17 and its mass number is 35 has 17 protons, 17 electrons and 18 neutrons.

The electrons in an atom are arranged around the nucleus in shells (energy levels). The electrons further away from the nucleus have more energy than those close to the nucleus. All elements in the same group of the periodic table have the same number of electrons in their outermost shell.

Neon and argon are in group 0 , are noble gases and have full outermost shells.

Metal atoms form positively charged ions because they attract one or more electrons when they combine with non-metals. Non-metal atoms lose electrons in the reactions forming negative ions. The oppositely charged ions attract each other. This is called ionic bonding. When non-metals combine with each other, they form covalent bonds. Their atoms share electrons.

Sodium atoms lose one electron when they combine with fluorine. Each fluorine atom gains one electron in the reaction. The name of the compound formed when sodium reacts with fluorine is sodium fluoride. F9 Na11, so F- Na+. Na + F = NaF

The reactant in the decomposition of calcium carbonate is calcium carbonate. The products are calcium oxide and carbon dioxide.

All symbol equations should be balanced to show that atoms cannot be created or destroyed in a chemical reactions and that the total mass of the products formed in a reaction is equal to the total mass of a reaction.

A mass of 8.4g of magnesium carbonate completely decomposes when heated. It made 4.0g of magnesium oxide. The total mass of carbon dioxide produced is 4.4g.

2Ca + O₂ = 2CaO

To make lots of calcium oxide, thermal decomposition is done in a…