2 Atoms, elements and compounds
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elements
simplest structure that cannot be broken down into smaller parts or changed into another substance.
Compound
a substance made from two or more different elements that have been chemically joined
mixture
a combination of two or more substances (elements or compounds) that are not chemically combined
atom structure
a central nucleus containing neutrons and protons surounded by electrons in shells
relative charges of proton, neutron and an electron
Electron is -1 Proton is +1 neutron is 0
relative masses of proton, neutron and an electron
Electron is 1/1835 Proton is 1 Neutron is 1
proton/atomic number
number of protons in the nucleus of an atom
mass/nucleon number
the total number of protons and neutrons in the nucleus of an atom
isotopes
different atoms of the same element that have the same number of protons by different numbers of neutrons
chemical properties of isotopes
isotopes of the same element have same chemical properties because they have the same number of electrons and therefore the same electronic configuration
relative atomic mass formula
(abundance x mass number)/100
cations
positive ions
anions
negative ions
ionic bond
a strong electrostatic attraction between oppositely charged ions
ionic compounds properties
high melting and boiling points good electrical conductivity when aqueous or molten and poor when solid
giant lattice structure of ionic compound
regular arrangement of alternating positive and negative ions
why do ionic compounds have high melting points?
have strong electrostatic forces of attraction between oppositely charged ions. Large amounts of energy are needed to break the many strong bonds.
why are ionic compounds a good conductor of electricty when liquid?
Because their ions are free to move from place to place
How are covalent bonds formed
when a pair of electrons is shared between two atoms leading to a full shell
why do simple molecular bonds have low melting and boiling points
The have weak intermolecular forces between molecules, low energy is required to break them
why do simple molecular structures have poor electrical conductivity
no free ions that can move
diamond
each carbon atom is covalently bonded to 4 other carbon atoms - tetrahedral - high m.p and b.p - no conduction of electricity
graphite
each carbon atom is covalently bonded with 3 other carbon atoms, resulting in a delocalised electron - flat sheets - high m.p and b.p - can conduct electricity
diamond usage
cutting tools, jewelery