Year 10 Chemistry Complete

Structure of atoms

• Atoms consist of a central nucleus consisting of protons and neutrons. 
• The nucleus is tiny compared to the size of the whole atom.
• The nucleus is surrounded by electrons in energy levels, or shells. 
• Atoms have no electric charge as the charges of the electrons and the protons coancel out to make the overall charge zero.
• The three sub-atomic particles are elctrons, neutrons and protons.
• Electrons have -1 charge and 1/1860 relative mass.
• Neutrons have 0 (neutral) charge but have +1 relative mass.
• Protons have a +1 charge and a relative mass of +1.
• The atomic number tells you the number of protons in an element. Since an atom's charge is zero, this means  that there are the same number of electrons as protons so the atomic number also tells you the number of electrons.
• The mass number tells you the sum of the number of neutrons and protons added. 
• The number of neutrons is calculated by doing the equation Mass number - Atomic number = Number of neutrons.
• It is the number of protons that decides what element something is, e.g Chlorine always has 17 protons.
• Isotopes are atoms with the same number of protons and electrons, but a different number of neutrons. For example, Chlorine 35 has 18 neutrons, with the standard 17 electrons and 17 protons, but Chlorine 37 has 20 neutrons as well as the standard 17 electrons and 17 protons.
• Ionic compounds
• Calcium atoms react with chlorine atoms to form the ionic compound calcium chloride. Calcium atoms each lose two electrons to complete an outer shell to form calcium ions. Chlorine atoms each gain one electron to form chloride ions. This means that calcium atoms react with chlorine atomes in the ratio of one calcium atom for every chlorine atom, making the chemical formula CaCl2.
• The elements in group one of the periodic table are called the alkalines. They are all metals. When any group one element reacts with a non-metal, an ionic compound is formed in which the metal ion has a positive charge (eg Li+, Na+, K+, Rb+, Cs+) as the metal atom loses one electron, taking away a negative charge so the charge goes from zero to one.
• The elements in group seven of the periodic table are called the halogens. They are all non-metals. When any group seven metal reacts with a metal, an ionic compound is formed in which the ion has a negative charge (e.g. F-, Cl-, Br-, I-, called hallide ions) as the non-metal gains an electron to give it a negative charge in addition.
• In these ionic compounds, a compound is always made.
• Ionic bonds are always giant and strong.
• Covalent bonding
• Everything in the universe wants to be stable. Hydrogen on its own is very unstable. It has one electron in its first shell, meaning it has an incomplete outer shell, which is why it is so unstable. 
• This means a hydrogen atom can bond to itself to create H2, so it then…