Chapter 3 - Bonding Flashcards
Describe the structure of ionic crystals
Ionic lattice structure with positive (cations) and negative (anions)
E.g. Each Na+ ions and Cl-
Describe the bonding present in ionic structures
Formed because of a transfer of e- from metal to the non-metal
Ionic bonds have STRONG ELECTROSTATIC attractions BETWEEN oppositely charged ions
What is the melting point of ionic structures?
High mp. because of the large number of strong electrostatic attraction between + and - charged ions, meaning the energy required to overcome these bonds is high
Do ionic structures conduct electricity?
Only when molten or in aq solution because the ions are free to move and carry charge
Are ionic substances soluble in water and why?
Yes
Because water is polar, the negative parts of the water are attracted to the positive metal ions and vice versa
The (smaller/larger) the ion and the (lower/higher) the charge on the ions the stronger the ionic bond
smaller
Higher
Positive ions are usually (larger/smaller) than the atoms from which they are formed
Negative ions are usually (larger/smaller)
Smaller
Larger
Give the formula for hydrogen carbonate, carbonate, ammonium, nitrate
(HCO3)- (CO3)2- (NH4)+ (NO3)-
Define a metallic bond
The electrostatic attraction between the sea of delocalised electrons and the positive metal ions in the lattice
Metals have (high/low) densities
High
Positive ions are packed tightly together
Why do metals conduct electricity?
In the sea of delocalised electrons the electrons are free to move, electric current flows because of the movement of electrons
Suggest why metals conduct heat
Because in the sea of delocalised e- the e- are close enough to transfer heat
Why are metals ductile and malleable?
Layered structure of the lattice, the layers can slide over one another without disrupting the bond
Top layer moves with the force applied to it
Strong attraction btwn sea of delocalised e- and positive metal ions holds the structure together
Most metals have (low/high) melting points
High
Relatively large regular structure with strong forces of attraction between the positive ions and delocalised electrons
This force of attraction has to be overcome which requires a lot of energy
What are the similarities and differences between simple molecular and macromolecular?
Both contain covalent bonds
Macromolecular are giant/larger
What are molecular covalent crystals? and give 2 examples
Solid molecular substances that form crystallin structures, don’t conduct electricity
e.g. iodine and ice due to the attractions
Name 3 properties of molecular covalent crystals
Low melting points
Brittle bc they don’t have strong bonds holding together like other crystalline substances
Don’t conduct electricity bc they have no charged free particles
Give 2 examples of macromolecular substances
Diamond
Graphite
What are allotropes?
Different forms of the same element in the same physical state (e.g. 2 allotropes of carbon are diamond and graphite
Describe the properties of diamond
has many strong cov bonds and rigid 3D structure
Very high melting point, bc of strong cov b which require a lot of energy to break
Each C atom is strongly bonded to four others in a tetrahedral arrangement
Bond angle 109.5
Don’t conduct heat or electricity as no charged particles that can move
Describe the main properties of graphite
- Conducts electricity due to delocalised electrons between the layers which can move and carry charge
- V high mp bc of its many strong covalent bonds which require a lot of energy to break
- Flaky as the force of attraction between the layers of carbon are weak so can be broken easily allowing layers to slide over each other
Describe the structure of graphite
Layered structure with weak forces of attraction between the layers
Each C atoms is bonded to 3 others in hexagonal arrangement w bond angle 120
Each C atom have 4 unpaired electrons so can form 4 covalent bonds
In diamond the 4th electron is used to bond but in graphite the 4th is used as a free electron
What are the TYPES of crystalline substances?
Metals
Ionic Compounds
Simple molecular
Macromolecular
Define electronegativity
The power of an atom to attract the pair of electrons in a covalent bond
What are the factors affecting electronegativity?
- Atomic radius
- Atomic number
- Shielding
What are the trends in electronegativity
Increases across a period
- Atomic radius decreases across a period, giving progressively stronger attraction between the positive nucleus and the two e- in the cov bond
-Nuclear charge increases across a period, increasing attraction for the electrons
Decreases down a group
- Atomic radius increases down a group, giving progressively weaker attraction btwn positive nucleus and cov bond electrons
- Shielding increases down a group
The greater the electronegativity difference the (more/less) polar the bond
More
A large difference in electronegativity means…
An ionic bond