Bonding Flashcards
Definition of ionic bonding?
Electrostatic attraction between positive and negative ions
In general where do you find ionic bonding?
Compounds made up of a metal and a non metal
How to draw ionic dot and cross diagrams?
Metal: Put symbol in brackets, and it’s charge in the top right
Non metal: Put symbol surrounded by outer shell showing which electrons are from which element, inside the brackets. Then put the charge at the top right
Definition of a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What’s a molecule?
A small group of atoms bonded together by covalent bonds
How to draw covalent molecule dot and cross diagrams?
Look at group number to determine how many electrons in outer shell of each element
Pair up unpaired electrons between atoms to form covalent bonds, using different symbols for each atoms electrons
How many electrons are in the outer shell of atoms after forming covalent bonds (ignoring hydrogen)?
8, the octet rule
What’s a covalent double bond?
Made up of 2 shared pairs of electrons
What’s a covalent triple bond?
Made up of 3 shared pairs of electrons
What’s a shared pair of electrons called?
A bonding pair
What’s a pair of electrons in the outer which aren’t being used in bonding called?
A lone pair
What’s a dative covalent bond?
A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
If there’s a dative bond what charge will be on the molecule?
A positive one, as an electron has been lost
What’s the definition of average bond enthalpy?
The average enthalpy change which takes place, when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species
What’s the relationship between average bond enthalpy change and the strength of the covalent bond?
A stronger bond will have a larger average bond enthalpy
What’s stronger a double or a single bond?
Double
What type of structure do metals have?
Giant- continuous structure in three dimensions
In metals why are the electrons in their valence shells held loosely?
Metals have relatively low ionisation energies, so metals are surrounded by delocalised electrons
What’s the general structure of a metal?
Lattice of positive ions, surrounded by a delocalised sea of electrons
Definition of metallic bonding?
The electrostatic attraction between positive metal ions and delocalised electrons
Why do metals have high melting and boiling points?
Strong electrostatic attraction between positive metal ions and delocalised electrons requires a lot of energy to break
why are metals Good conductors of electricity when solid?
Delocalised electrons can move and carry charge
why are metals Good conductors of electricity when molten?
Delocalised electrons and positive ions can move and carry charge
Why are metals insoluble in water or non polar solvents?
Strong electrostatic attractions between positive ions and delocalised electrons require a lot of energy to break, which isn’t available
How many electrons in metals or donated into the sea of electrons?
All of them, so as you go up the groups more electrons are donated
Why does the melting points of period 3 metals increase as you go up the groups?
The charge of the metal ion increases, and the number of delocalised electron per ion increases as well, this means stronger electrostatic attraction between metal ions and delocalised electrons, so more energy required to break them
Also more delocalised electrons per ion, means better at conducting electricity, so has a greater capacity of carrying charge
Metals are malleable, what does that mean?
Can easily be bent in to different shapes
Metals are ductile, what does that mean?
Can be drawn into a wire
Why are metals ductile and malleable?
Layers of ions can easily slide over each other
What are alloys?
mixtures of metals
What metals are present in brass?
Cu and Zn
What metals are present in stainless steel?
Fe and Cr
How does an alloy make a metal harder?
Each metal ion is a slightly different size, so layers of ions do not slide over each other as easily
What is the arrangement of ions in an ionic solid described as?
Giant ionic lattice
What is a giant ionic lattice?
Continuous lattice arrangement of + and - ions in three dimensions
Why do ionic compounds have high boiling and melting points?
Strong electrostatic forces of attraction between positive and negative ions requires a lot of energy to overcome
Why are ionic compounds non conductors of electricity when solid?
The ions are fixed in lattice so cannot move and carry charge
Why are ionic compounds good electricity conductors when molten or dissolved in water?
The ions are no longer fixed in lattice, so are able to move and carry charge
Why do ionic compounds have good solubility in water?
Oxygen atom in water molecules is attracted to and surrounds the positive ions in the lattice, and the hydrogen atoms in the water molecules are attracted to and surround the negative ions. This breaks down the ionic lattice and dissolves the compound
Why are ionic compounds brittle?
The slight movement of a layer of ions brings positive ions next to other positive ions, and the same for negative ions. This causes repulsion and the structure breaks apart
Factors which lead to high melting points in ionic compounds?
Higher charges in ions
Small ionic radius
What’s a simple molecular structure?
Small units containing a definite number of atoms, and a definite molecular formula
Do simple molecular structure have a high or low melting/ boiling points and why?
Low, weak intermolecular forces between molecules require little energy to break
Are simple molecular structure electrical conductors?
No, have no free mobile electrons or charged particles to carry charge
What’s a giant covalent structure?
Billions of atoms held together to form a network of strong covalent bonds
Do giant covalent structures have high or low melting/boiling points? Why?
High, Strong covalent bonds need to be broken, which requires a lot of energy
Are giant covalent structures electrical conductors?
No, have no free mobile electrons or charged particles to carry charge
Structure of diamond?
Each carbon forms 4 covalent bonds, making it very hard
Is diamond an electrical conductor?
No, no free electrons to carry charge
Is diamond hard?
Yes, tetrahedral structure of each carbon atom spreads force throughout the structure, strong covalent bonds require a lot of energy to break
Structure of graphite?
Each carbon forms 3 covalent bonds, creating layers which are free to slide over each other
Can graphite conduct electricity?
Yes, delocalised electrons in layers are free to move and carry charge
Is graphite hard?
No, weak intermolecular forces between layers can be broken, and layers can slide over each other
Why is graphite a good lubricant?
Strong layers but weak London forces between the layers which need little energy to break. The layers can slide over each other easily
What does the valence shell electron pair repulsion theory state?
Electron pairs repel each other
The repulsion between lone pair- lone pair> to lone pair- bonded pair > bonded pair- bonded pair
Features of a compound which has 2 bonded pairs around the central atom?
Orbital arrangement: Linear
Bond angle:180 degrees
Features of a compound which has 3 bonded pairs around the central atom?
Orbital arrangement: Trigonal planar
Bond angle: 120 degrees
Features of a compound which has 4 bonded pairs around the central atom?
Orbital arrangement: Tetrahedral
Bond angle 109.5 degrees
Features of a compound which has 3 bonded pairs and 1 lone pair around the central atom?
Orbital arrangement: Trigonal Pyramid
Bond angle: 107 degrees
Features of a compound which has 2 bonded pairs and 2 lone pairs around the central atom?
Orbital arrangement: V shaped or bent
Bond angle: 104.5
Features of a compound which has 6 bonded pairs around the central atom?
Orbital arrangement: Octahedral
Bond angle: 90 degrees
What does intermolecular forces mean?
Forces between molecules
Where would you find intermolecular forces?
Simple covalent lattice
What are the 2 types of van der waal forces?
London forces (induced dipole to dipole)
Permanent dipole-dipole interactions
What’s the only attractive intermolecular force that acts in non polar molecules?
London forces
How do London forces arise?
Electrons in molecules are constantly moving, at any instant the distribution may not be symmetrical, resulting in an instantaneous temporary dipole.
This dipole induces dipoles in neighbouring molecules, and leads to an attraction between neighbouring charges in the dipoles.
These attractions are London forces
What’s a dipole?
a pair of equal and oppositely charged or magnetized poles separated by a distance
What affects the strength of London forces?
The more electrons that are in the molecule, the stronger the fluctuations in the electron cloud, and the greater the instantaneous dipole to induced dipole forces
For molecules with the same amount of electrons, the greater the contact area between the molecules, the stronger the induced dipoles that develop. So unbranched molecules have stronger London forces than branched molecules, as there contact area is greater
definition of electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
What are the elements with the largest electronegativity from highest to lowest and there pauling value?
F 4.0, O 3.5, N 3.0, Cl 3.0
What is a permanent dipole?
A small charge difference which doesn’t change across a bond, with partial charges on the bonded atoms
What’s a polar covalent bond?
A bond with a permanent dipole, having positive and negative partial charges on the bonded atoms
What’s a polar molecule?
A molecule with an overall dipole, having taken into account any dipoles across bonds, and the shape of the molecule
What’s a hydrogen bond?
A strong dipole-dipole attraction between an electron deficient hydrogen atom of NH,OH, HF on one molecule, and a lone pair of electrons on a highly electronegative atom (N, O or F) on a different molecule
What symbol do you use for a slight charge?
Delta δ
How do you draw hydrogen bonds?
Staggered verticle lines
What’s responsible for the higher than expected melting and boiling points of water for a molecule of its size?
Hydrogen bonding
Why does ice float on water?
It’s less dense than water, meaning for a given volume, there are less molecules of H20 in ice than water, this is because when water freezes the molecules are pushed further apart due to the hydrogen bonding
How is hydrogen bonding relevant in proteins?
Responsible for secondary structure of proteins eg. a-helices, and b-sheets
What’s responsible for the double helix structure in DNA?
Hydrogen bonding, adenine to thymine, and cytosine to guanine
