Structure and Bonding Flashcards
(45 cards)
What is a chemical bond and what are the three examples?
A chemical bond is a force that holds particles together in a material
- covalent
- ionic
- metallic
What is a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded electrons
Each atom donates a valence electron to the bond to achieve a noble gas configuration
What is a dative covalent bond?
A covalent bond where only one of the bonded toms donates both electrons being shared from a lone pair
What is electron pair repulsion theory?
- shape of a simple molecule or ion is determined by the number of bonding and lone pairs of electrons around the central atom
- electron pairs repel each other but lone pairs repel each other more
What is the bond angle of a linear covalent molecule?
180
2 bonding pairs
What is the bond angle of a trigonal planar covalent bond?
120
3 bonding pairs
What is the bond angle of a tetrahedral covalent bond?
109.5
4 bonding pairs
What is the bond angle of an octahedral covalent bond?
90
Six bonding pairs
What is the bond angle of the pyramidal covalent bond?
107
3 bonding pairs
1 lone pair
5 outer shell electrons down the central atom
What is the bond angle of the non-linear covalent bond?
104.5
2 bonding pairs
2 lone pairs
6 outer shells around the central atom
Name the shape of, and state the bond angle of BF3 molecule and explain why BF3 has this shape?
- electron pairs repel to get as far apart as possible
- 3 bonding pairs and no lone pairs
- 120 bond angle, trigonal planar shape
What are the three types of intermolecular force?
- Induced dipole dipole interactions (IDDI)
- permanent dipole dipole interactions (PDDI)
- hydrogen bonds
What are induced dipole dipole interactions?
IDDI are temporary and occur between non polar molecules
- temporary as the electron density is constantly changing
- weakest intermolecular force
- symmetrical molecules with no overall dipole interaction through IDDI
How do IDDI arise?
- electrons in a molecule are constantly moving and at any one instant the electron distribution may be unsymmetrical
- produces a temporary dipole in that molecule
- if another molecule approaches the molecule with a temporary dipole an opposite dipole is induced into the adjacent molecule
What increases the strength of IDDI?
- increases as the number of electrons in a molecule or atom increases (I2 has stronger IDDI than F2 as it has more e-)
- increases as surface contact of the molecules or atoms increases (branched molecules can form less IDDI so are weaker)
What are polar molecules?
The uneven distribution of electrons in a bond
What are PDDI?
Covalent bonds between different atoms where one atom has a stronger attraction for the shared electrons than the other
What is electronegativity?
Th ability of an atom to attract the atom to attract the bonding electrons in a covalent bond
The higher the number, the greater the attraction
What is the trend of electronegativity?
- increases across a period
- increases up a group
- highest electronegativity = F
- lowest electronegativity = Cs
What happens when a molecule has polar bonds, but is symmetrical?
- the dipoles will cancel each other out and there is no overall permanent dipole making the molecule non-polar
- anything with a lone pairs isn’t symmetrical
Why is CCl4 non polar?
- although the 4 bonds are polar the molecule is symmetrical
- the dipoles act in opposite directions
- dipoles cancel each other out
Why is water polar?
- H2O is polar as it it unsymmetrical
- dipoles do not cancel each other out
- oxygen is more electronegative than hydrogen
What is hydrogen bonding?
Intermolecular bonding between molecules containing N, O, or F and the H atom of -NH, -OH, or -HF
What is the melting point of simple covalent molecules?
- low melting + boiling points
- atoms held together by strong covalent bonds which aren’t broken when melted or boiled, but the molecules are held together by weak intermolecular forces which require little energy to break
