Bonding Flashcards
What does mono atomic mean?
Elements exist as single atoms
Group 8
Do not bond with other atoms
Insoluble in water
Do not form ions or conduct electricity
Weak forces between atoms so low melting and boiling points
Bigger atoms have stronger forces between atoms and so a higher melting point
What is simple molecular ?
Simple molecules made of non metals
Covalent bonds between atoms in molecule
Low melting point as weak forces between molecules
Do not conduct electricity as there are no mobile ions
Melting point increases as the size of the molecule increases as the size of intermolecular forces increases
They are isnoluble
What is giant covalent?
Covalent bonding
Insoluble
High melting and boiling points as strong covalent bonds need to be broken
Melting point increases when the strength of covalent bonds increase
What are some examples of giant covalent molecules?
Diamond, silicon ,silicon dioxide which do not conduct electricity
Graphite and graphene which do conduct electricity
What do you know about ionic bonding?
Very high melting point
Do not conduct electricity when solid
Conduct electricity when a liquid so molten or dissolved
Soluble
Why do ionic compounds have very high melting points?
Strong electrostatic forces of attraction between oppositely charged ions
Smaller ions and higher charges increase the strength of the ionic bond which increases the melting point
Why do ionic compounds not conduct when solid?
As the ions are fixed
Why do ionic compounds conduct electricity when molten or dissolved?
As the ions are feee to move
What is metallic bonding?
Bonding between metals
High melting point
They conduct electricity
Metals are insoluble
Why do metallic compounds conduct electricity?
Delocalised electrons carry a charge through the structure
Why do metallic compounds have high melting points?
The attraction between positively charged ions and the delocalised negatively charged electrons
State what you know about ionic bonding
Atoms make bonds between each other by using their outer electrons
They want to gain a more stable electron configuration which is achieved by gaining a full outer shell of electrons
Describe the structure of sodium chloride.
Giant ionic lattice
Strong electrostatic forces of attraction between positive sodium ions Na+ and negative chloride ions Cl-
Must name the ions and not just say oppositely charged ions
Why are ionic compounds solid at room temperature?
Strong electrostatic forces of attraction between positive ions and negative ions
Why do ionic compounds not conduct electricity when solid but do when molten or dissolved?
In a solid ions cannot freely move around and they are fixed
When aqueous ions are feee to move and carry a charge
DO NOT TALK ABOUT ELECTRONS HERE
Why are ionic compounds brittle?
Like charges repel and so the structure shatters
External force may move ions in the lattice and like ions may touch and then repel
When are ionic bonds strongest?
When the size of the ion is smallest and the charge on the ion is high
State what you know about covalent bonding
A shared pair of electrons
Electrons are joined together by electron clouds
Double bonds can form but triple bonds are rare
What is a co ordinate bond?
A covalent bond where both of the electrons in the bond come from just one of the atoms involved
It’s also called a dative covalent bond
What is special about a co ordinate bond?
The atoms that accept electrons are electron deficient and so don’t have a full outer shell
The donating atom donates a lone pair of electrons which is a non bonding pair of electrons
The strength of a co ordinate bond I the same as a regular covalent bond
State what you know about metallic bonding.
Metals can easily lose up to 3 outer electrons
The metal ions are compactly arranged in a lattice- Giant metallic structure
Lots of atoms are joined together
Electrons become part of a delocalised sea of electrons
As you go across the group ionic size decreases and ionic charge increases
What are properties of metallic compounds?
Malleable and ductile
Very strong
High melting points due to strong attractions
What are atoms held together by?
Held together between positive and negative charges of ions
Ionic bonding
What is electronegativity?
The power of an atom to attract the electron density of a covalent bond towards itself
What does electronegativity depend on?
Nuclear charge of the atom
Distance between the nucleus to the outer electrons
Shielding of nuclear charge by inner electrons
State what else you know about electronegativity.
One atom may be better at pulling electrons towards itself than another
This results in one atom having a greater share of electrons in the bond
The atoms with a greater share of electrons is said to be more electronegative
What are electrons considered as?
Clouds of charge
Electron density is used to describe the way charge is distributed
How does electronegativity increase?
Up a group
If an element has a high ionisation energy it also has a high electronegativity
Electronegativity also increases across a period
What is used to measure electronegativity?
The Pauli scale
4.0 is given as the largest electronegativity possible
What are the most electronegative atoms?
Fluorine
Oxygen
Nitrogen
Chlorine
What is polarity?
The unequal sharing of electrons in a bond
If the electron sharing is equal the bond is described as non polar
If the electron cloud is distributed unevenly it is described as polar
What are partial charges used to represent?
If two atoms that are bonded together have a difference in electronegativities and the bond is polar
They are described as delta positive and delta negative
What will be delta negative?
The highest electronegativity
What will be delta positive?
The lowest electronegativity
What is special about some molecules?
A molecule can be made up of several polar bonds but may be non polar overall
Molecules are symmetrical there is no overall polarity and the electron cloud is shared evenly over the whole molecule
What are ionic and covalent bonding two extremes of?
A continuum of bonding
Type of long line
What determines where a compound lies on this scale?
Differences in electronegativity between elements
Elements are not always purely ionic or purely covalent
When will a compound be ionic?
A compound containing elements of very different electronegativity and so very large electronegativity difference
Less than 1.7
What will make a compound purely covalent?
A compound containing elements of similar electronegativity and hence a small electronegativity difference
What are intermolecular forces?
Act between separate molecules or atoms and are weaker than intramolecular bonds
Thy can be strong enough to hold molecules close enough together for them to be a liquid or even a solid
What are the intramolecular bonds?
Covalent
Ionic
Metallic
What are the intermolecular forces?
Van deer waals forces
Dipole dipole forces
Hydrogen bonding
What is the strongest type of intermolecular force?
Hydrogen bonding
What is the weakest type of intermolecular force?
Van deer waals forces
What do all molecules have acting between them?
Van deer waals forces
What do only certain molecules have acting between them?
Dipole dipole forces
Hydrogen bonding
State what you know about dipole dipole forces.
Occur between molecules that contain an overall dipole which is polar molecules
Dipole refers to a molecule where the charge is shared unevenly
These forces are permanent
Lots of molecules join like this
Opposite charges attract
What is used to show any intermolecular force in a Diagram?
A dotted line
State what you know about van deer waals forces.
Sometimes called instantaneous dipole or induced dipole
This force acts between all molecules or separate atoms
Even if other intermolecular forces are present
Very weak
How do the strength of van deer waals forces increase?
As you go down a group
Bigger molecule means a stronger van deer waals force
Electrons are constantly moving around which leads to an uneven distribution
State what you know about hydrogen bonding.
One tenth the strength of a covalent bond
Strongest intermolecular force
Some character if dipole dipole interactions and some character of dative covalent bonding
What does hydrogen bonding have to have?
A lone pair of electrons which are non bonding involved
When does hydrogen bonding occur?
When a molecule has a:
Very electronegative atom like fluorine, oxygen or nitrogen
Hydrogen atom covalently bonded to this electronegative atom
How are bonds in plane drawn?
Going up and outward to the side so a straight line
How are bonds sticking out of the paper towards us drawn?
A wedge coloured or shaded in
How are bonds going backward into the paper drawn?
A dotted wedge
What is used to determine what shape a molecule is?
The valence shell electron pair repulsion theory
What is the vsepr based on the idea of?
Each pair of electrons around an atom repels all other pairs of electrons
Pairs of electrons spread themselves around the atom as far from each other as possible to minimise repulsion
Repulsion between different types of electron pairs have slightly different strengths of repulsion
What is an important thing to remember?
A lone pair repels more than a bonded pair
What is a bonding pair of electrons?
The two shared electrons are in a covalent bond
What is a lone pair of electrons?
When two electrons in a pair are not involved in bonding
They are also known as non bonding pairs
What is the shape of the molecule with 2 bonding pairs?
Linear with a bond angle of 180 degrees
What is the shape of the molecule with 3 bonding pairs?
Trigonal planar with a bond angle of 120 degrees
What is the shape of the molecule with 4 electron bonded pairs?
Tetrahedral with a bond angle of 109.5 degrees
What is the shape of the molecule with 5 bonding pairs?
Trigonal bipyramidal with bond angles of 120 and 90 degrees
What is the shape of the molecule with 6 bonding pairs?
Octahedral with a bond angle of 90 degrees
Hat is the shape of the molecule with 2 bonding pairs and 1 lone pair?
Bent v shape with a bond angle of 118 degrees
What is the shape of the molecule that has 3 bonding pairs and 1 lone pair?
Trigonal pyramidal with a bond angle of 107 degrees
What is the shape of the molecule with 2 bonding and 2 lone pairs of electrons?
Bent v shape with a bond angle of 104.5 degrees
What is the shape of the molecule with 4 bonding and 1 lone pair?
Trigonal pyramidal or see saw with bond angles of 119 and 89 degrees
These angles are in different places depending which of the two shapes you draw
What is the shape of the molecule with 3 bonding and 2 lone pairs of electrons?
Trigonal planar or T shape with a bond angle of 120 or 89 degrees again depending upon which one you draw
What is the shape of the molecule with 5 bonding pairs and 1 lone pair of electrons?
Square pyramid with a bond angle of 89 degrees
What is the shape of the molecule with 4 bonding and 2 lone pairs of electrons?
Square planar with a bond angle of 90 degrees
Also known as a right angle
