chem topic 2

• The atomic number (Z) represents the number of protons.
• Ions are charged particles formed when an atom gains or loses electrons.
• Isotopes are atoms with different numbers of neutrons but the same number of protons.
• Isotopes have different atomic masses but the same chemical properties as they have the same number of protons.
• Isotopes of an element have different numbers of neutrons in their nuclei but the same number of protons.
• Elements contain protons that are stable and unchanging in the nucleus of an atom.
• Atoms can gain or lose electrons to form positive or negative ions.
• noble gases are unreactive because they have a full outer shell
• alkalis and halogens react aggressively
• elements on the left side of the periodic table tend to be metals while those on the right tend to be non-metals
• The first electron shell can hold 2 electrons
• the second electron shell can hold up to 8 electrons
• group 1 are the alkali metals and they are soft and have low melting and boiling points
• group 2 are called the alkaline earth metals
• group 7 are called the halogens and they are very reactive
• group 0 elements are called noble gases and are non-metals. They are inert and do not react with other elements.
• the charge of a proton is +1 and the mass is 1
• the charge of a neutron is 0 and it has a relative mass of 1
• the charge of an electron is -1 and the mass is 0.0005
• an ion has a charge whereas an atom does not, atoms are neutral
• for ions the number of electrons is different to the number of protons
• group 1 atoms form 1+ ions
• group 3 atoms form 3+ ions
• group 7 atoms form 1- ions
• democritus suggested indivisible small blocks called atoms
• john dalton suggested the billiard ball model
• jj thompson discovered the electron and created the plum pudding model
• ernest rutherford found the atom is mostly empty, the nucleus is positive and that mass is concentrated in the nucleus
• neils bohr discovered electrons are on shells
• james chadwick discovered neutrons
• isotopes have different numbers of neutrons but same amount of protons
• mass number = protons + neutrons
• the atomic number tells us how many protons an element has
• relative atomic mass = average mass of all naturally occurring isotopes
• the amount of electrons that can be on the third shell is 8
• 18 electrons can be stored on the 4th shell