Chapter 6 shapes of molecules and intemolecular forces Flashcards
1
Q
Describe the electron pair repulsion
A
- an electron has a negative charge so electron repel one another
- electron pairs surrounding a central atom determines the shape of the molecule of ion
- electron repel on another so are arranged as far apart as possible
- arrangement of electron pairs minimises repulsion and holds the bonded atoms in a definite shape
- different numbers of electron pair result in different shapes
2
Q
Describe the shape of the molecule in methane
A
- four bonded pari of electrons surround the central carbon atom
- four electron pairs repel on another as far apart as possible in a 3D shape
- result in a tetrahedral shape
- four equal H- C-H bond
- resilting in angle of 109.5
3
Q
What is the difference between repulsion of bonded pairs and lone pairs
A
- lone pair of electrons is closer to central atom and occupies more apce
- lone pair repelling more strongly than a bondin pair
4
Q
Describe the shape in ammonia and water
A
- four electron pairs around central atom repair one another as far apart as possible into a tetrahedral arrangement
- lone pairs repel more strongly than bonded pairs
- lone pair repel bonded pairs slightly closer together decreasing bond angle
- bond angle is reduced by 2.5 degrees celcius for each lone pair
5
Q
Describe a tetrahedral shape
A
- 4 bonded pairs
- 0 lone pairs
- 109.5 degrees
6
Q
Describe a pyrimidal shape
A
- 3 bonded pairs
- 1 lone pairs
- 107 degrees
7
Q
Describe a non linear shape
A
- 2 bonded pairs
- 2 lone pairs
- 104.5
8
Q
Describe the molecular shape of other number of electron pairs
A
- electron pairs around central atom repel each other as far apart as possible
- greater number of electron pairs the smalled the bond angle
- lond pairs of electrons repel more strongly than bonded pairs of electrons
9
Q
Describe the linear shape in carbon dioxide
A
- 4 bonded pairs around the central carbon atom arranged as two double bonds whcih count as two bonded regions
- two bondede regions repel one antoehr as far apart as possible
- giving it a linear shape
10
Q
Describe a linear shape
A
- 2 electron pairs
- 180 degrees
- no lone pairs
11
Q
Describe a trigonal planar
A
- 3 electron pairs
- 120 degrees
- 0 lone pairs
12
Q
Describe the octahedral shape
A
- 90 degrees
- 6 electron pairs
- 0 lone pairs
13
Q
Describe the shape of an ammonium ions
A
- four bonded pairs
- same number of bonded pairs of electrons around the central atom as methane molecule
- same tetrahedral hape and bond angle of 109.5
14
Q
What is electronegativity
A
- the shared pair of electron in covalent bond may now experience more attraction from one of the bonded atoms than the other
- the attraction of a bonded atom for the pair of electrons in a covalent bond
15
Q
When does bonded electron pair is not shared evenly
A
- nuclear charges are different
- atoms may be different sizes
- shared pair of electrons mau be closer to one nucleass than the other
16
Q
How is electronegativity measured
A
- decreases down group
- increases across a period
- noble gas has no electronegativity
- fluorine has the highest of four
17
Q
How does the electronegativity difference determine bond type
A
- covalent - 0
- polar covalent -0-1.8
- ionic greater than 1.8
18
Q
What are non polar bonds
A
- bonded electron pair is shared equally between the bonded atoms
- the bonded atoms are the same of have same or similar electronegativity
- like C-H
19
Q
What are polar bonds
A
- bonded pair is shared unequally between the bonded atoms
- bond polar when bonded atoms are different and have differnt electronegativity values
20
Q
Describe the how H-Cl is polar
A
- hydrogen has a lower electronegativity than chlorine
- chlorine has a greater attraction for the bonded pairs of electrons than the hydrogen atom resulting in a polar covalent bond
- it becomes polarised and a seperation of opposite charges called a dipole
21
Q
What is a permanent dipole
A
- dipole in a covalent bond that does not change
22
Q
Why is H2O polar
A
- two O-H bond each have a permanent dipole
- two dipoles act in different diections not exactly oppose one another
- overall oxygen has a partial negative charge and hydrogen end has a partial positive charge
23
Q
Why is CO2 polar
A
- two C=O bonds each have a permanent dipole
- two dipoles acti in opposite directions and exactly oppose one another
- over the whole molecule dipoles cancel and overall dipole is zero
24
Q
Describe the types of intemolecular forces
A
- induced dipole-dipole interactions (london forces)
- permanent dipole-dipole interaction
- hydrogen bonding
25
What are intemolecular forces
* weak interactions between dipoles of different molecules
26
What are london forces
* weak intemolecular forces exist between all molecules
* act between induced dipoles
27
How do induced dipoles occur
* movement of electron produces a changing dipole in a molecule
* at any itant an instantaneous dipole will exist position is constatly shifting
* instantaneous dipole induces a dipole on neighbouring molecules
* induced dipole induces further dipoles on neighbouring molecules whcih then attract one another
* only temporary
28
How is the strength of london forces determined
* larger instantansous and induced dipoles
* greater induced dipole-dipole interactions
* stronger attractive forces between molecules
* larger numbr of electrons laeger induced dipoles
* more energy needed to overcome the intemolecular forces increasing the boiling point
29
Wat is the difference in boiling point between polar and non polar molecules
* flourine molecules are non polar only have london forces between molecules
* polar molecules have london forces and permanent dipole-dipole interactions between molecules
* extra energy is needed to break the additional permanenet dipole-dipole interactions between polar moleciles
* boiling point of polar molecules is higher than non polar molecules
30
Describe simple molecular structures
* made up of simple molecules
* in solid state simple molecular lattic
* molecules are held by weak intemolecilar forces
* atoms wtihin each molecule are bonded together strongyl by covalent bonds
31
Why do simple molecules have low melting and boiling points
* weak intemolecular forces can be broken by energy at low temperatures
* only weak intemolecular forces break and covalent bonds are strong and do not break
32
Describe the solubility of simple molecular structure in non polar molecules in non polar solvents
* when non polar intemolecular forces form between molecules and solvent and interactions weaken and inttermoleculae forces in simple molecular lattice and it breaks and compound dissolves
33
Describe the solubility of non polar simple molecular substances in polar solvents
* when a simple molecule is added to polar solvent little interaction between molecules and lattice
* intemolecular bonding within polar solvnt too strong to be broken
34
Describe the solubillity of polar simple molecules
* polar substances maydissolve in polar solvents ass the polar olte molecules and the polar solvent molecules can attract each other
* solubility depends on strength of the dipole
* ethanol contaiin polar and non o
* polar so can dissolve in both
35
Describe the electrical conductivity of simple molcules
* no mobile charged particles in simple molecules
* no charged paarticles that can move
36
What is a hydrogen bond
* special type of permanent dipole - dipole interaction
* between an electrongative atom with a lone pair of electrons oxygen,nitrogen and fluorine
* a hydrogen atom attatched to an electronegative atom
* acts between a lone pair of electrons on an eectronegative atom and hydrogen atom in another molecule
* strongest time of intemolecular forces
37
Why is solid ice less dense than liquid water
* hydrogen bond holds water molecules apart in an open lattice structure
* water molecules in ice fruther apart than in water
* solid ice less dense than liquid water and floats
38
Why does water hae a high melting and boiling point
* hydrogen bonds are extra forces above london forces
* appreciate quantity of energy needed to break hydrogen bonds in water
* when ice lattic breaks rigid arraangement of hydrogen bonds in ice is broken so when water boils at 100 degrees hydrogen bond is broken completley
39
What are other anomalous properties of water except for high melting and boiling points and ice being less dense than liquid water
* high surface tension
* high viscosity
* not wet allow insects walk on pond surface
