Bonding Flashcards
How are ions formed?
-ions are formed when electrons are transferred between elements that have a large difference in electronegativity i.e metal and non-metals
- metals lose electrons while non-metals gain them.
how do ions arrange themselves?
- a regular lattice of negative and positive ions form
- they arrange themselves in such a way that minimises repulsion.
What is ionic bonding?
ionic bonding occurs when two or more ions combine to form an electrically neutral compound
- the positive cation ‘loses’ a valence electron so that it has a full valence charge but a positive charge
- the negative cation ‘gains’ a valence electron so that it has a full valence shell but a negative charge
-electrons are not shared between the two cations but they are attracted to each other due to differences in their charge.
what are the properties of metals in ionic bonding?
- metals are always the cation
- metals on the left side of the periodic table have 2,3, or 4 valence electrons. it is very easy to lose thee and become positive ions
what are the properties of non-metals in ionic bonding?
- non-metals with the exception of hydrogen are always the anion
- all have 4 or more valence electrons so it is very easy for them to gain a full outer shell and become negative.
what are polyatomic ions?
- ions that are made up of more than one type of atom e.g. ammonium
what are the properties of ionic compounds?
- high melting and boiling points due to many electrostatic forces of attraction between positive and negative ions
- conducts electricity when dissolved in water or molten
- in water, the bonds dissociate leaving lots of ions to carry charge
what is metallic bonding?
- metallic bonding consists of a lattice of positively charged ions surrounded by a sea of delocalised electrons producing a very strong force of attraction between the oppositely charged particles.
- ions that are larger produce a weaker force of attraction due to their atomic radius.
what is delocalisation?
Delocalization refers to the phenomenon where electrons are not confined to a single atom or covalent bond. It occurs when electric charge is spread over more than one atom.
what are the properties of metals?
- good conductors of electricity and heat due to delocalised electrons and vibrational energy
- strong
-malleable and ductile
high melting and boiling point
what is a covalent bond?
- between non-metals
- atoms share electrons to attain full outer shells
- the nuclei of each atom are attracted to the shared pair of electrons
can covalent molecules have multiple bonds?
- yes
- two shared electrons make a single bonds
- four makes a double bond
six makes a triple bond
how do you show covalent bonds?
- a line with a dot above and a cross below it showing the shared pairs of electrons.
what is a non-bonding pair?
electrons that are not used in a bonding pair form lone pairs.
what is a coordinate bond? ( dative covalent)
- these form when both of the electrons in the shared pair come from a single atom
- it is indicated using an arrow
- e.g NH3+
what is the electron pair repulsion theory?
- a theory that predicts the shape of simple molecules.
1. determine the central atom
2. determine the group of the central atom, this should tell you its outer electrons
3. look at the charge on the molecule, this affects the outer e
4. look at how many bonds are in the molecule
5. add up the outer number of elections and the charge of the molecule
6. divide this number by two to get the number of electron pairs
7. work out any bond pairs and lone pairs
8. figure out the shape and bond angles remembering that electrons repel each other
for every lone pair present around the central atom how much does the bond angle decrease?
2.5.
what is the bond angle in linear molecules?
180
what is the bond angle and name of a shape with 3 bond pairs?
- 120
- trigonal planar e,g boron trichloride
what is the bond angle and name in a shape with 4 bond pairs?
- 109.5
- tetrahedral
what is the bond angle and name in a shape with 5 bond pairs?
- 120 and 90
- trigonal bi-pyramid
what is the bond angle and name in a shape with 6 bond pairs?
-90
- octahedral
what is the order of repulsive power in electron pairs?
- lone pair - lone pair
- lone pair-bonding pair
- bonding pair-bonding pair
what effects do lone pairs have on the shape of molecules
- removing lone pairs makes the bond angles bigger as there is more space for the bonding pairs to occupy
what is the sharing of electrons like in our covalent substances?
- even sharing of electrons
- equally distributed between both nuclei
what is the sharing of electrons like in our ionic substances?
- the electrons are totally transferred from one atom to another
- the ions are distinct from each other
how do we measure the bond character(in terms of electronegativity?
- we use electronegativity to measure the ionic or covalent- ness of a bond
- from 1 - 4
what is electronegativity?
a measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond
what factors affect electronegativity?
- the size of the nuclear charge
- distance between the nucleus and outer shell
- shielding
what are the trends in electronegativity across a period?
- electronegativity increases
- all electrons are at the same distance from the nucleus
- protons are being added
- atoms are smaller
- shielding is the same
what are the trends in electronegativity down a group?
- electronegativity decreases
- increase in atomic radius
- increase of shielding
what are the most electronegative elements?
F , O, N S, Cl .Br
What happens in bonds with big differences in electronegativity?
- big differences in electronegativity means the bond will be polar
- one of the atoms holds the electrons closer to itself in the bond
- one end of the bond will be slightly negative and the other slightly positive
- we use delta symbols to show where the areas are slightly negative / positive
can a molecule be polar if it symmetrical?
No because all the positive and negative regions would cancel each other out
What are intermolecular forces?
forces that exist between molecules
- VDW D-D H
- these are all weaker than a covalent bond
What is the order of force strength of intermolecular forces?
- VDW
- D-D
- H
what is an instantaneous dipole?
- electrons are constantly moving around at any one moment there could be more electrons at one end of the atom just through chance
- this results in the formation of slightly negative region at one end of the atom and a slightly positive region at the other end
what is an induced dipole?
- the instantaneous dipole can cause the formation of an induced dipole in neighbouring atoms
What are van der Waals forces?
the weak force of attraction between the neighbouring oppositely charged ends of two instantaneous dipoles
- all atoms and molecules posses these forces
What are dipole forces?
- dipoles on different molecules can interact
- this causes an attractive force between different molecules
- these are permanent
What is a dipole moment?
- some covalent bonds are polar
- the arrangement o polar bonds can result in a molecule becoming polar overall
what is hydrogen bonding?
- the strongest type of intermolecular force
- only form between NFO (most electrostatic)
- the lone pairs on these atoms forms a bond with a hydrogen from another molecule, shown with a dotted line
What is the importance of hydrogen bonding?
- ice is less dense then water
- water has a much higher melting and boiling point than expected
- protein folding
- DNA base pairing
- Enzyme reactions
What are the four types of crystal structure?
- ionic
- metallic
- macromolecular
- simple molecular
What are the properties of Ionic crystal structures?
- high melting and boiling points as the electrostatic forces holding the ionic lattice together are strong
- can conduct electricity when molten or in solution as the ions are no longer held in a lattice they are free to move and carry a flow of charge
- brittle as when an external force hits the lattice alternating layers are distorted , like charges repel so the lattice is broken apart into fragments.
What are the properties of metallic crystal structures?
- good conductors of electricity
- sea of delocalised electrons are is able to move and carry a charge
- malleable as layers of positive ions are able to slide over each other
- high melting and boiling points as foA between positive ions and delocalised electrons is so strong
- solid at room temp
What are the properties of simple molecular structures?
- covalently bonded molecules held together with weak van der Waals forces
- poor conductors as their structures contain no charged particles
-low melting and boiling points
What are the properties of macromolecular crystal structures?
- atoms covalently bonded into a giant lattice structure
- high melting point due to strong covalent bonds
- rigid due to strength
- e.g. diamond is four carbons bonded to four other carbons making it the hardest strongest materials known
-e.g. graphite carbon bonded to 3 others in flat sheet free electrons move in between layers meaning it can conduct electricity
