chemical bonding Flashcards
compound
substance that is made up of two or more DIFFERENT elements combined together chemically
octet rule
when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell
an ion
a charged atom or group of atoms
an ionic bond
the force of attraction between oppositely charged ions in a compound
transition metal
one that forms at least one ion with a partially filled sublevel
molecule
group of atoms joined together. It is the smaller particle of an element or compound that can exist independently
valency of an element
defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
electronegativity
a measure of the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
electronegativity differences
- difference > 1.7 indicates ionic bonding in a compound
- difference ≤ 1.7 indicates covalent bonding in a compound
the value of electronegativity
- decreases down groups in Periodic Table. (Bc of increasing atomic radius, screening effect of inner electrons)
- increases across table (bc of increasing nuclear charge, decreasing atomic radius)
the most electronegative element
F
halogens
decrease in reducing power down group due to drop in electronegativity values
noble gases
- have 8 electrons on their outer shell + are quite stable
- generally unreactive
uses of noble gases
helium
argon
helium
used in airships as it is lighter than air
not as light as hydrogen (twice as heavy per volume) but does not burn
argon
most common noble gas
used to fill normal light bulbs to stop them imploding
limitations of the octet rule
hydrogen
lithium
transition metals
valency
the number of bonds an atom makes when it reacts
how to get valency
- can be worked out calculating the number of electrons an atom needs to lose/gain to have 8e⁻ on outer shell
- can be predicted from periodic table
examples of valency numbers
ammonia (contains only nitrogen and hydrogen)
methane (contains only carbon and hydrogen)
calcium bromide
silicon fluroide
transition metals (info)
- transition elements have variable valency
- form coloured compounds
- used as catalysts
- exceptions: zinc (Zn), scandium (Sc)
ionic bonding
-transfer of electrons
-ions are formed
-ionic bonding usually between Groups I and II (metals)
and groups VI and VII (non-metals)
cation
positive (+)
anion
negative (-)
crystal lattice
ionic substances usually form a structure called a crystal lattice
eg of crystal lattice
NaCl
why ionic substances form crystals
ionic substances form crystals bc positive ions attract negative ions in all directions
what shape do crystals form?
a lattice structure
characteristics of ionic substances
- strong forces between ions -> v. hard to break up the lattice structure
- high melting + boiling points
- usually solid at room temp
- cannot conduct electricity when solid (ions not free -> move and carry electricity)
- most dissolve in water (when dissolved, ions can conduct electricity)
examples of everyday ionic substances
- table salt (sodium chloride NaCl)
- fluoridation in water to prevent tooth decay (sodium fluoride NaF)
complex ions table
in hardback
covalent bonding
formed when atoms share electrons
eg. hydrogen molecule, chlorine molecule
types of covalent bonds
single
double triple
covalents bonds - single
1 pair of electron shared
eg. H₂
covalents bonds - double
2 pairs of electrons shared
eg. O₂
covalents bonds - triple
3 pairs of electrons shared
eg. N₂
bonding pairs
shared electron pairs that form covalent bonds