Bonding Flashcards
What is ionic bonding?
the force of attraction between oppositely charged ions
How are the ions formed in ionic bonding?
the ions are formed by the transfer of electrons from metal atoms to non-metal atoms
What layer of electrons are involved in ionic bonding?
only the outer electrons
What happens to metal atoms in ionic bonding?
they lose electrons to form cations (+)
What happens to non-metal atoms in ionic bonding?
they gain electrons to form anions (-)
What state are ionic compounds in when at room temperature?
solids with high melting and boiling points
What does the strength of the attractive forces depend on in ionic bonding?
the size and charge of the ions
The electrostatic forces increase in strength as…
-the charge on the ion increases
-the size of the ion decreases
What is a crystal?
a solid with a regular shape which contains particles organised in a regular structure
How are the ions arranged in a giant ionic lattice?
in a regular repeating pattern
What type of diagram should you draw in an exam to represent an ionic compound?
a ball and stick diagram
What other diagram can you draw to represent ionic compounds?
space filling
What are the advantages of space filling diagrams?
they are 3D models
they accurately show the space taken up by each ion
What are the disadvantages of space filling diagrams?
difficult to see the the structure of the whole ionic lattice clearly
bonds are not shown clearly
What are the advantages of ball and stick diagrams?
they are 3D models
they allow you to see the structure of the whole ionic lattice clearly as bonds are shown as lines
What is the limitation of ball and stick diagrams?
not actually representative of the space taken up by the ions
Why do ionic crystals have high melting points?
because they contain a very large number of strong ionic bonds which require a lot of energy to break
What are ionic crystals like?
hard and brittle
What are ionic crystals usually soluble in?
water
Why do ionic crystals not conduct electricity?
because the ions are not free to move and carry a current
When can ionic compounds conduct electricity and why?
when an ionic compound is melted or in solution it can conduct electricity because the ions are free to move and carry the current
Why are ionic compounds always neutrally charged?
the charges on the positive and negative ions balance out
What is the coordination number?
the number of ions that one particular ion in a lattice is in contact with
Why are ionic compounds soluble in water?
in solution an ionic compound will fully ionise and so positive and negative ions can fit between water molecules arranged such that oppositely charged regions interact
Describe in detail the structure and bonding in a sodium chloride crystal
bonding-
1 sodium atom transfers 1 electron to 1 atom of chlorine
this results in the formation of a Na+ ion and a Cl- ion
the oppositely charged ions are attracted to one another by strong ionic bonds
these strong electrostatic forces require a lot of energy to break
structure-
there is a strong electrostatic attraction between the Cl- and the Na+ ions, and they are arranged in a giant ionic lattice
each ion is by 6 other oppositely charged ions
the crystal is cubic and has a coordination number of 6
What is a covalent bond?
a single shared pair of electrons
What is covalent bonding between?
two non metals
What is a lone pair of electrons?
non-bonded pairs of electrons in a compound
What is a co-ordinate/dative bond?
co-ordinate/dative bonds are formed when one atom contributes both of the electrons needed for the covalent bond from a lone pair on the donor atom
What is octet expansion?
when atoms have more than 8 electrons in it’s outer shell
How are co-ordinate bonds represented?
an arrow
What are the two types of covalent structure?
simple molecular
giant macromolecular
What are some examples of simple molecular structures?
water/ammonia/iodine/oxygen
What are some examples of giant macromolecular structures?
diamond/graphite/silicon dioxide/silicon
What do simple molecular structures consist of?
small molecules
The covalent bonds within the molecules are strong, but…
the forces of attraction between the molecules are weak
Why do simple molecular compounds have low melting and boiling points?
the amount of energy required to break the weak intermolecular forces is small
What state are simple molecules in at room temperature?
gases or volatile liquids
Why are simple molecules non-conductors?
no ions or free electrons present in simple covalent compounds
What is the structure of solid iodine like?
the I2 molecules are held together by van der Waals forces between the adjacent molecules
the distance between the iodine atoms within a molecule is less than the distance between iodine atoms in adjacent molecules
in an iodine crystal the molecules are arranged in a regular repeating pattern
Why does iodine have a low melting/boiling point?
because the weak van der Waals forces require little energy to break
What are allotropes?
different forms of the same element in the same physical state
What is the bonding in diamond?
each carbon atom is covalently bonded to 4 other carbon atoms in a giant covalent structure
the co-ordination number of the carbon atoms is 4
the arrangement of bonds is tetrahedral
Why is the melting/boiling point of diamond so high? (3500C)
a very large amount of energy is needed to break the large number of strong covalent bonds
Why is diamond a non-conductor of electricity?
because all of the outer electrons in carbon atoms are involved in bonding so there are no free electrons to carry a current
What is the bonding and structure in graphite?
each carbon atom is covalently bonded to three other carbon atoms
the co-ordination number of the carbon atoms is 3
the arrangement is trigonal planar
the trigonal planar arrangement leads to the formation of layers in which the carbons form regular hexagons
What is the bond angle of diamond?
109.5
What is the bond angle of graphite?
120
Why can graphite conduct electricity?
each carbon atom in graphite forms three covalent bonds, leaving 1 delocalised free electron between the plates of covalently bonded carbon atoms
the electrons are free to move BETWEEN LAYERS NOT UP AND DOWN
Why is graphite soft?
it has weak van der Waals forced between the adjacent layers that means they can easily slide over each other
Why does graphite have high melting/boiling points?
lots of energy is needed to break the large number of strong covalent bonds
What is metallic bonding?
metallic bonding is the force of attraction between the delocalised electrons and the positive metal ions in a lattice
What is the giant metallic lattice?
closely packed positive metal ions surrounded by a sea of delocalised electrons
Why are do metallic ions have a high melting/boiling point?
due to the strong metallic bonds between ions
A large amount of energy is needed to…
remove a metal atom from the attraction of the delocalised electrons
The strength of metallic bonding depends on…
the size and charge of the positive ions/the number of mobile electrons per atom
Metallic bonding strength increases as…
charge on the positive metal ion increases
the size of the metal atom decreases
the number of delocalised electrons per atom increases
The electrical conductivity of a metal increases as…
the number of delocalised electrons per atom increases
What are delocalised electrons also responsible for? (nothing to do with the electrical conductivity)
for the metals ability to reflect light
Why are metals malleable and ductile?
the planes of ions can slide over each other
What are metallic crystals usually made from?
repeating units which tend to be hexagonal or cubric
What is magnesium’s crystal structure?
a close-packed hexagonal structure, coordination number of 12
What is electronegativity?
an atom’s ability to withdraw electron density from a covalent bond
Across a period electronegativity…
increases because-
atomic radius decreases
the positive nuclear charge increases with similar shielding
Down a group electronegativity…
decreases because-
increase in atomic radius
more shielding
Which elements are the most electronegative and their values?
N-3.0/O-3.5/F-4.0
In terms of electronegativity, diatomic molecules are always…
non-polar as the atoms have the same electronegativity value
The greater the difference of the electronegativity value, the more…
polarised the bond is
Why are some covalent bonds polar?
when atoms of different electronegativity are bonded together the more electronegative atom withdraws the electron pair more strongly so has a greater share of the electrons, making it polar
Why are some molecules (like CCL4/CO2) non-polar even though they contain polar bonds?
these molecules are spherical and therefore the polar bonds within them cancel each other out leaving the molecule non-polar as the electron cloud is symmetrical
What is the Pauling scale?
a relative measure of how well an atom can attract electrons
Why do group 0 not have electronegativity values?
they do not form covalent bonds
When atoms with SIMILAR electronegativity are bonded together what occurs?
covalent bonding and covalent substances are formed
When atoms with A LARGE DIFFERENCE in electronegativity are bonded together, what occurs?
ionic bonding and ionic substances are formed
