Chapter 3 - Bonding Flashcards
define ionic bonding
the result of electrostatic attraction between oppositely charged ions
how does ionic bonding occur
it can only occur between a metal and a non metal
the metal atom loses valence electrons, the non-metal atom gains the valence electrons lost by the metal
this interaction forms 2 ions, a positive metal ion and a negative non-metal ion
the opposite charges between ions form strong electrostatic forces between the ions
the force is the bonding
what are valence electrons
outer shell electrons
why do atoms which bond ionically lose or gain electrons
to achieve a noble gas structure
why do ionically bonded atoms want to have noble gas structures
because it makes their arrangements more stable
how do ionic compounds exist naturally
in a giant lattice
what are the physical properties of an ionically bonded structure
they are brittle
they conduct electricity when molten or aqueous only
they have high boiling and melting points (usually solid at room temp)
why are ionic compounds brittle
because when the lattice of positive and negative ions distorts, it is easy for same charge ions to come into contact and repel, making the structure break
why do ionic compounds conduct electricity when molten only
charged ions can carry charge only if they are free to move, in solids the ions only vibrate on the spot and cannot freely move
why do ionic compounds have high melting and boiling points
ionic compounds exist in a giant lattice, this means that there are very many bonds needed to be broken, so a lot of energy needs to be supplied to the substance
what is a covalent bond
a covalent bond can be defined by the bond formed between two or more non metal atoms (same or different) which is the result of sharing some valence electrons to achieve a noble gas structure
how do covalent bonds form
two or more non-metal atoms share some of their valence electrons to form a covalent bond
how many electrons does a double covalent bond share
4 electrons total
2 pairs of electrons
what are the properties of a covalently bonded substance (substance with a molecular structure)
low melting and boiling points
poor conductors both solid and molten
what sort of bonds hold together the molecules in a molecular substance
intermolecular bonds
describe the electrostatic bonds in a molecule
electrostatic bonds of attraction form between the positive nucleus and the negative electrons
the nuclei of the bonded atoms repel each other as they have the same charge
the attractive forces must be stronger than or equal to the repulsive forces for the molecule to form
why do molecular substances have low melting and boiling points
the electrostatic forces within the molecule are strong,
however the intermolecular forces between individual forces are weak and don’t require much energy to overcome
why are molecular substances poor conductors in any state of matter
each covalently bonded molecule has a neutral charge because no ions are formed
therefore there are no charged particles to carry charge even when the molecules are mobile
describe co-ordinate or dative bonding
this is a type of covalent bond which only occurs when a pair of electrons is provided by one atom but shared between two
a co-ordinate bond is indistinguishable from a standard covalent bond once bonded
what is a lone pair of electrons
a pair of electrons on an atom which are both from the same atom and are not being used in a bond
what is a bonded pair of electrons
a pair of electrons in which each is from a different atom
what is an electron deficient atom
an atom which does not have a full outer main level of electrons
how are dative bonds written on a dot and cross diagram
the lone pair is indicated and an arrow drawn outwards points to the atomic symbol of the electron deficient atom
the charge of the electron deficient atom is indicated
how are dative bonds written usually
an arrow pointing towards the electron deficient atom
if there is a charge, square brackets surrounding the entire molecule and the charge of the electron deficient atom is indicated in the top right corner of the brackets
what type of atom will usually form positive ions
metal atom
what type of atom will usually form negative ions
non-metal atoms
define a metallic bond
a metallic bond is the attraction between positive metal ions which have lost their outer shell of electrons and the negative sea of delocalized electrons lost by the metal positive metal ions
describe the electrons lost by the metal ions
when they are lost, they become delocalized meaning that they are free to move throughout the lattice of positive ions
what makes metals conductive
the “sea” of electrons is free to move throughout the positive metal ion lattice and carry charge throughout it
describe the conduction of electricity by a metal
when one electron joins the sea of electrons from the negative terminal, another electron leaves the sea at the positive terminal so that the total number of electrons within a metals electron cloud is constant
what are the properties of a metallically bonded substance
high conductivity as solids and liquids
high melting and boiling points
malleable and ductile
why do metals have high melting and boiling points
there is strong attraction between the metal ions and the sea of electrons, which makes them difficult to separate
additionally, they have giant structures, making the energy needed to break all the bonds substantially high
what does the strength of a metal depend on
the charge on the ion
the size of the ion
how does the charge on the ion change a metals strength
the higher the positive charge, the more delocalized electrons per ion
therefore the electron cloud is greater when there are more electrons and the electrostatic attraction between the positive ions and the electrons is stronger
how does the size of the atom change the metals strength
the smaller the ion, the closer the electrons are to the nucleus, therefore the bond is stronger
why are metals malleable and ductile
when the metal is distorted, the ions will still be in the same environment as they were before the distortion so the structure doesnt break and can be bent into different shapes easily
define electronegativity
the power of an atom to attract the electron density in a covalent bond towards itself
what does electron density mean
the way negative charge is distributed in a molecule
what scale is used to measure electronegativity
the pauling scale
it goes from 0 to 4
what is the most electronegative element
flourine
what does electronegativity depend on
the nuclear charge
the distance between the nucleus and the outer shell electrons
the shielding of nuclear charge by electrons in inner shells
how is electronegativity affected if the atom is smaller and why
name the 4 most electronegative atoms in order
flourine, oxygen, nitrogen, chlorine
comment on the trends in electronegativity in the periodic table
as you go up a group, the electronegativity increases because the outer shell electrons are closer to the nucleus
as you go across a period, the electronegativity increases because the nuclear charge increases while the lower level shells remain the same
what is polarity about in covalent bonding
the unequal sharing of electrons that are bonded together in a covalent bond
it is a property of a covalent bond
describe the polarity of a molecule made up of one type of atom
the molecule is non polar because the shared electrons are attracted to all atoms equally and hence stay in the middle of the bond
what does non polar mean for a molecule
the molecule has no poles
the charge of the shared electrons is shared equally in between all the atoms in the molecule
how can you identify if a molecule made of 2 individual atoms is polar or non polar
if they are the same, it is non polar
if they are different, it is polar
why are molecules made of 2 different individual atoms considered polar
because each atom has a different electronegativity
leading the shared electrons to be attracted to one atom more than the other
increasing the electron density (negative charge) around one pole of the molecule than the other
what does a delta symbol indicate when written with the formula of a molecule
delta plus and delta minus symbols indicate less than an “electrons worth” of charge towards that atom in the molecule
what are the three types of intermolecular force, in order of weakest to strongest
van der Waals
Dipole-dipole forces
Hydrogen bonding
what is a dipole moment
the dipole moment sums up the effect of the polarity of all the bonds in a molecule
what are the 2 things which may occur with a molecule with more than one polar bond
the dipoles cancel and there is no dipole moment
or they reinforce eachother
what does the dipole moment depend on
the shape of the molecule
what does it mean for the dipoles to cancel
the molecule has the same charge on either side
what molecules do dipole dipole forces act between
molecules with permanent dipoles (molecules with a slightly negative charge on one side and a slightly positive one on the other)
how does the attraction between dipoles work
the positive pole of a molecule is attracted to the negative pole of another molecule, and so on
what are van der waals forces
instantaneous charges within atoms or molecules which produce weak electrostatic attractions between other atoms or forces
how can a neutral atom be a dipole
because the electrons within an atom are always moving, they could be in a different location every instant
this means that an atoms electrons may converge more on one side of the atom in an instant creating a temporary dipole from the atom
when an atom becomes a temporary dipole, what happens?
it affects the electron distribution in other nearby atoms so that they are attracted to the dipole atom for an instant by becoming dipoles (since the electrons will be repelled from the electron side of the original dipole)
the new dipole causes additional atoms to become attracted and become dipoles and causes a kind of chain reaction in surrounding atoms where they instantaneously become dipoles
what are two key facts about how van der waals forces behave
van der waals forces act between all molecules or atoms at all times
they are in addition to other intermolecular forces
what will affect the strength of van der waal forces between atoms or molecules
the dipole is caused by the changing position of the electron cloud surrounding the atom, so an atom with more electrons will have a larger electron could and stronger instantaneous dipoles
what trends in the periodic table do van der waals forces account for
the boiling points of the noble gases increase as the atomic numbers of the noble gases increase
the boiling points of hydrocarbons increase with increased chain length.
why does water not have dipole-dipole forces between its molecules
the oxygen atoms have lone pairs of electrons
the hydrogen atoms are highly electron deficient
what conditions must be present for a hydrogen bond to occur
a very electronegative atom with a lone pair of electrons covalently bonded to a hydrogen atom
why are they hydrogen atoms in water highly electron deficient
oxygen is very electronegative so it attracts the shared electrons towards it
the hydrogen atoms are positively charged and really small, meaning that their electric field is very strong
what atoms are electronegative enough for hydrogen bonding
oxygen, fluorine, nitrogen
describe a linear molecule
bond angles: 180
bonding pairs: 2
lone pairs: 0
describe a trigonal planar molecule
bond angles: 120
bonding pairs: 3
lone pairs: 0
describe a bent linear molecule
bond angles: 118
bonding pairs: 2
lone pairs: 1
describe a tetragedral molecule
bond angles: 109.5
bonding pairs: 4
lone pairs: 0
describe a pyramidal molecule
bond angles: 107
bonding pairs: 3
lone pairs: 1
describe a bend (v-shaped) molecule
bond angles: 104.5
bonding pairs: 2
lone pairs: 2
describe a trigonal bipyramid
bond angles: 90 and 120
bonding pairs: 5
lone pairs: 0
OR
bonding pairs: 3
lone pairs: 2
describe a square based pyramidal molecule
bond angles: 90
bonding pairs: 4
lone pairs: 1
describe an octahedral molecule
bond angles: 90
bonding pairs: 6
lone pairs: 0
OR
bonding pairs: 4
lone pairs: 2
what does macromolecular mean
a covalent substance in which the covalent bonds extend throughout the compound
these substances have high melting oiints since the covalent bonds require a lot of energy to break
