Chemical Bonding Flashcards
What is a coumpound
A substance that is made up of two or more different elements combined together chemically
What is the octet rule
When bonding occours, atoms tend to reach an electron arrangement with eight electrons in the outermost shell
What are expections to the Octet rule
Transition elements dont obey the octet rule and often have more or less than 8 electrons in the outer shell
Elements near helium tens to have 2 electrons in the outer shell
What is an ion
A charged atom/ group of atoms
What is a postive ion called
Cations
What is a negative ion called
Anions
What is an ionic bond
The force of attraction between oppositly charged ions in a compound
What do you use to show the formation of ionic bonding
Bohr diagrams, dot and cross diagrams
What structure do ionic compounds have
Crystal lattice structure
What are crustal lattice structures dertimined by?
X-ray crystallography
Charateristics of ionic compounds
Hardness- hard substances due to strong ionic bonds and crystal lattice structures.
Melting and boiling points- high melting and boiling points due to strong ionic bonds and crystal lattice structure.
Conduction of electricity.Dont condict electricity in solid state but do conduct electricity in the molten state or when dissolved in water as the ions are free to carry the charge.
What are elements placed in the transition metal block but not transition elements, and why are they an expection?
Sc and Zn are not transition metals.Sc and Zinc have different properties to the other transition elements
what is a transition metal
An elements that forms at least one ion with a partially filled d sublevel.
What are the properties of transition elements
Transition elements have varaible valency. Sc only forms SC3+ ions and zn only forms Zn 2+ ions
transition elements usually form colourful compounds, scandium and zinc only form white compounds.
Transition elements are widely used as catalysts. Sc and zn show little catalytic activity.
varable valency
the number of atoms of different elements in which a certain element can combine with.
What is a covalent bond
One which involves that sharing of electrons between atoms.
What is a molecule
Agroup of atoms joined together. Its the smallest partical of an element or compound that can exist independently
What can molecules only be used for
Covalent compounds
What is the Valency of a element
The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
What is a single bond
one pair of electrons are shared between two atoms
What is a double bond
two pairs of electrons are shared between two atoms
What is a triple bond
three shared pairs of electrons
what is a group of organic compounds called
Aldehydes
What is a sigma bond
A sigma bond is fored due the head-on overlap of two orbitals
(All single covalent bonds can be describes as a sigma bond)
What is formed when two atomic orbitals overlap
Molecular orbital
What is a pi bonf
A pi bond is formed due to sideways/ lateral overlap of P orbitals
Are Sigma bonds stronger or Pi bonds stronger
There is less overlap between orbitals in a pi bond, therefore it is weaker than a sigma bond
What does a single covalent bond consist of
1 sigma bond
What does a double covalent bond consist of
1 sigma and 1 pi bond
What does a triple covalent bond consist of
1 sigma and two pi
Charateristics of ionic and covalent compounds
Their differences
Ionic
Contains a network of ions in the crystal
usually hard and brittle
high melting and boiling points
usually solid at room temperture
conduct electricty when dissolved in water or molten
Covalent
contain individual molecules
usually soft
usually have low melting and boiling points
usually liquid or gasses at room temperature
dont conduct electricity ( no ions present)
What is VSEPR
Valance shell electron pair repulsion theory states the shape of a molecule depends on the number of pairs of electrons in the valence shell of the central atom
Why do electrons repel eachother
electrons are negativily charged, the electron pairs repel eachother and arrange themselves in space to be as far apart as possible.
what are loan pairs
Both electrons come from the same atom
What are bond pairs
each electron comes from a different atom
What is a dative corrdinate bond
Special type of covalent bond where one atom supplies both the electrons
Eg. NH4+
A molecule has 4 electron pairs,4 bond pairs,0 loan pairs what shape it it?
Tetrahedral
A molecule has 3 electron pairs,3 bond pairs,0 loan pairs what shape it it?
Trigonal planer
A molecule has 2 electron pairs,2 bond pairs,0 loan pairs what shape it it?
Linear
A molecule has 4 electron pairs,3 bond pairs,1 loan pairs what shape it it?
Pyramidial
A molecule has 4 electron pairs,2 bond pairs,2 loan pairs what shape it it?
V-shaped / bend
What is the bond angle of a tetrahedral
109.5
What is the bond angle of a trigonal planer
120
What is the bond angle of a linear
180
What is the bond angle of a pymidial
107
What is the bond angle of a v-shaped
104.5
Which molecule shapes are not symmetrical
Pyramidial and v-shaped
What is electronegativity
The relative force of attractions two atoms in a molecule have for a shared pair of electrons in a covalent bond
What can electronegivity be used to predict
Polarity of covalent bonds
perdict which compounds are ionic and which ones are covalent
In a covalent between two of the same atoms, how are the electrons shared
the pair of electrons are shared equally between the two atos in the molecule
Im a covalent bond bwetween two different atoms, how are the electrons shared
more attracted to one atom than another.
What is a charge indicated by?
Delta δ
What does the word polar mean
the bonding electrons aren’t shared equally. There is a partial postive and partial negative charge on the molecule.
These partial charges are seperated by some distance,
What is the term pure covalent bond
refers to a covalent bond where there is equal sharing of electrons
What does a moleule need to have in order to be a polar molecule
It cant be symmetrical
Why is water clearly a polar molecule
Water is v shaped, cant be symmetrical.
warer is a good solvent. most ionic substances and most polar covalent substances dissolve in water. Opposite charges are attracted towards eachother.
What does a EN difference of >1.7 indicate?
Ionic bonding
What does a EN difference of 0.4 -1.7 indicate?
Polar Covalent bond
What does a EN difference of < (or equal) 0.4 indicate?
Non polar covalent bond
What is the demostrating polarity used to show
to show if a compund (usually a liquid)is polar.Water is polar. ( has tempoary postive charges associated) water will deflect when a postively or negativily charged rod comes near. The H postive will be attracted towards the negativily charged rod.Similarly, the O (negative) will be sttracted to th negativitly charged rod.
Cyclohexane is an organic compound that is non-polar (no deflection
What is Intramolecular bonding and give examples
boing that takes place within a molecule
Ionic, Polar covalent, non polar covalent
What in Intermolecular bonding and give example
Forces of attraction between molecules
van der waals forces, dipole-dipole forces, Hydrogen bonding
What are Van der waals forces
weak attractive forces between molecules resulting from the formation of tempoary dipoles
Where do Van der Waals forces exist between
All non-polar molecules, Nobel gas atoms
Properties of van der waals forces
Have low boiling points (often gasses at room temperture) Insoluble in water( they are non polar and dont form hydrogen bonds with water)
Very weak attractive force
As the atom size increases, Van de waals forces increase in strenght, why?
the number of electrons present increases (bigger atomic number)
Number of tempoary dipoles formed increases.
The strenght of van der waals forces increases.
bigger the molecule/atom, higher the boiling point
What are dipole dipole forces
Forces of attraction netween the negative pole of one molecule an the postive pole of another
diople diople forces exist between…
all polar molecules
which polar molecules do dipole dipole forces not exist betweeen
H2O,HF,NH3
Properties of dipole-dipole forces
Dipole dipole forces are stonger than van der waals forces.
substances with dipole dipole forced between their molecules have highter melting and boiling points.
What is hydrogen bonding
Hydrogen bonds are particular types of dipole dipole attractions between moleules in which hydrogen atoms are bonded to nitogen, oxygen or fluorine
How does hydrogen bonding work
The hydeogen acts as a bridge between two electronegative atoms in seperate molecules. Flurinr, oxygen and nitrogen are very small electronegative elements. gives the molecules strong polarity
Properties of hydrogen bonding
Strongest intermolecule force.
higher boiling points and melting point.
Gives increased solubility in water.
H2O has a higher boiling point than HF and NH3, why?
H2O has twice as many haygrogen bonds between its molecules (HF)
Greater electronegivity value, greater
dipole (more polar)(NH3)
Hydrogen bonding in everyday life
Ensures water is liquid at room temp so life can exist on earth.
Synthetic clothing- bullet proof vests/protective clothing.
hydrogen bonds in wool help it absorb water. hydrogen bonds in water give it a high surface tension.
What does the hydrogen bonding in water allow it to do?
gives water a unusually high boiling point (ensures water is liquid at room temp)
Gives water a high water tension.
(water to flow against gravity in plants)
Ensures ice is less dense than water
(fish can survive in lakes in the winter)
