C1 notes

Atoms and elements

nucleus

• contains protons and neutrons
• protons are positively charged
• neutrons have no charge
• the nucleus has a positive charge

electrons

• negatively charged
• occupy shells around the nucleus

• atoms have no charge
• the number of protons always equals the number of electrons
• if electrons are added or removed, the atom becomes charged and becomes an ion
• the number of protons decides what type of atom it is
• if a substance only contains one type of atom it's called an element

The periodic table

• atoms can be represented by symbols
• elements with similar properties form columns
• vertical columns are called groups
• all of the elements in a group have the same number of electrons in their outer shell
• the elements in group 0 are the noble gases. This means that they're stable and unreactive. They have eight electrons in their outer shell except helium.

Electron shells

• electrons always occupy shells
• the lowest shells are always filled first
• 1st shell= 2 electrons
• 2nd shell= 8 electrons
• 3rd shell= 8 electrons
• in most atoms the ouer shelll is not full and this makes the atoms want to react to fill it
• to find the electronic structure of an element, list the number of electrons in each shell

Compounds

• when different elements react, atoms form chemical bonds with other atoms to form compunds
• making bonds involves giving away, taking, or sharing electrons
• a compound which is formed from a metal and a non metal consists of ions
• the metal atoms lose electrons to form positive ions and the non metal atoms gain electrons to form negative ions
• the opposite charges mean they're strongly attracted to each other. This is called ionic bonding
• a compound formed from non-metals consist of molecules. Each atom shares an electron with another atom- a covalent bond
• the properties of a compound are totally different from the properties of the original elements

Formulas and reactions

• a formula shows what atoms are in a compound
• atoms aren't lost or made in chemical reactions
• balanced symbol equations show the atoms at the start (the reactants)
• and the atoms at the end (the products) and how they're arranged
• the mass of the reactant=the mass of the product

Balancing equations

• you can balance the equation by putting numbers in front of the formulas where needed
• find an element that doesn't balance and pencil in a number to try and sort it out
• see where it gets you. It may create another imbalance-if so, just pencil another number and see where that gets you
• carry on chasing unbalanced elements and it'll sort itself out pretty quickly

Materials and properties

• melting point- the temperature where the solid materials turns to liquid
• strength- how good a material is at resisting a force
• tensile strength- resisting a pulling force
• compressive strength- resisting a pushing force
• stiffness- how good a material is at not bending
• hardness- how difficult it is to cut into a material

Properties of common materials

• plastics- hard, strong, stiff, some are low density, some…