C2 atoms, elements and compounds Flashcards
define element
- chemical substance
- cant be broken down into simpler substances
- composed of one type of atom only
define compounds
- substance made of 2 or more elements
- chemically bonded together
define mixture
- 2 or more chemical substances found together
- not chemically bonded
describe the structure of an atom
- central nucleus (containing neutrons and protons)
- surrounded by electrons in shells
relative charge of a proton
+1
relative mass of a proton
1
relative mass of a neutron
1
relative charge of a neutron
0
relative mass of an electron
negligible
relative charge of an electron
-1
define proton number
number of protons in nucleus of an atom
another word for proton number
atomic number
define mass number
total number of protons and neutrons in nucleus of an atom
another word for mass number
nucleon number
max number of electrons in innermost shell
2
max number of electrons in shells (except innermost)
8
what are elements in group VIII known as
noble gases
electrons in outer shell of group VIII?
full
correlation between group number and number of outer shell electrons
they are equal
correlation between occupied electron shells and period number
equal
define isotopes
- different atoms of same element
- same number of protons but different numbers of neutrons
why do isotopes of the same element have the same chemical properties
- same number of electrons
- therefore same electronic configuration
what is the force which occurs in a chemical bond
electrostatic force
why does chemical bonding occur
so all atoms involved achieve an electronic configuration with a full valence shell, which is highly stable
what is a cation
positive ion
what is an ion
- electrically charged particle
- formed when atom loses/gains electrons
what is an anion
a negative ion
what is an ionic bond
- strong electrostatic attraction
- between oppositely charged ions
properties of ionic compounds:
- high melting/boiling point
- good electrical conductor when aqueous/molten
- poor electrical conductor when solid
- generally soluble in water
what is the structure of ionic compounds
giant lattice structure
- regular arrangement
- alternating positive and negative ions
why does an ionic compound form a lattice structure
- electrostatic forces of attraction between alternating oppositely charged ions
- act in all directions
- to make giant 3d lattice
why is the melting/boiling point of ionic compounds high
- strong electrostatic force of attraction in all directions
- more thermal energy required to break bonds and turn substance to liquid
how does charge on ion impact melting point of ionic compound
higher charge on ions, higher the melting point
why cant ionic compounds conduct electricity while solid
- ions in giant 3d lattice unable to move freely
- because held tg by strong electrostatic forces of attraction
- ions are unable to carry charge
why can ionic compounds conduct electricity while molten/aqueous
- ions are able to move
- carry a charge
how is a covalent bond formed
- pair of electrons is shared between 2 atoms
- leading to noble gas electronic configurations
properties of simple molecular compounds
- low melting/boiling points
- poor electrical conductivity
why do simple molecular compounds have low melting/boiling points
- intermolecular forces between molecules weak
- not much energy needed to overcome
relationship between mass of molecules and boiling/melting point
- larger molecules have greater number of weak intermolecular forces
- therefore require more energy to separate molecules
- therefore melting/boiling point higher
why are simple molecular compounds poor electrical conductors
- do not have any charged particles which can move through structure
- therefore charge does not flow
what is the structure of diamond
- each carbon atoms shares 1 electron with 4 other carbon atoms
- to make giant repeating network of covalently bonded carbon atoms
uses of diamond and why
- cutting tools
- extremely hard substance
why is diamond so hard
made up of many strong covalent bonds in a giant structure
what is the structure of graphite
- comprised of layers
- each layer made up of carbon atoms, each bonded to 3 other atoms
- delocalised electrons can move freely across layers
- stacks of layers held tg by many weak intermolecular forces
define allotrope
alternative forms of an elemental substance
uses of graphite and why
- lubricant (layers can slide over each other)
- electrode (good conductor of electricity)
why can the layers in graphite slide over each other
- layers have weak intermolecular forces holding tg
- forces are weak
why is graphite a good conductor of electricity
- has delocalised electrons
- which can move freely throughout structure and carry electric current
describe metallic bonding
- electrostatic attraction
- between positive ions in giant metallic lattice and sea of delocalised electrons
properties of metals
- good electrical conductivity
- malleable
- high melting/boiling point
why do metals have high melting/boiling point
- metallic lattice held tg by strong electrostatic forces of attraction
- a lot of energy needed to separate metal atoms
why are metals good electrical conductors
- delocalised electrons in metallic lattice
- free to move throughout structure
why are metals malleable
- regular layers, practically identical (all ions same size and distance)
- when force applied, layers are able to slide past other layers
why will aluminium have a higher conductivity than sodium
- one aluminium atom delocalises 3 electrons in metallic bonding
- compared to only 1 in sodium
- more delocalised electrons = higher conductivity
