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Chemistry Module 2 > Chapter 6 shapes of molecules and intemolecular forces > Flashcards

Chapter 6 shapes of molecules and intemolecular forces Flashcards

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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
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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
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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
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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
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5
Q

Describe a tetrahedral shape

A
  • 4 bonded pairs
  • 0 lone pairs
  • 109.5 degrees
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6
Q

Describe a pyrimidal shape

A
  • 3 bonded pairs
  • 1 lone pairs
  • 107 degrees
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7
Q

Describe a non linear shape

A
  • 2 bonded pairs
  • 2 lone pairs
  • 104.5
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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
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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
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10
Q

Describe a linear shape

A
  • 2 electron pairs
  • 180 degrees
  • no lone pairs
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11
Q

Describe a trigonal planar

A
  • 3 electron pairs
  • 120 degrees
  • 0 lone pairs
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12
Q

Describe the octahedral shape

A
  • 90 degrees
  • 6 electron pairs
  • 0 lone pairs
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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
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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
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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
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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
Q

What are intemolecular forces

A
  • weak interactions between dipoles of different molecules
26
Q

What are london forces

A
  • weak intemolecular forces exist between all molecules
  • act between induced dipoles
27
Q

How do induced dipoles occur

A
  • 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
Q

How is the strength of london forces determined

A
  • 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
Q

Wat is the difference in boiling point between polar and non polar molecules

A
  • 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
Q

Describe simple molecular structures

A
  • 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
Q

Why do simple molecules have low melting and boiling points

A
  • 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
Q

Describe the solubility of simple molecular structure in non polar molecules in non polar solvents

A
  • 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
Q

Describe the solubility of non polar simple molecular substances in polar solvents

A
  • 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
Q

Describe the solubillity of polar simple molecules

A
  • 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
Q

Describe the electrical conductivity of simple molcules

A
  • no mobile charged particles in simple molecules
  • no charged paarticles that can move
36
Q

What is a hydrogen bond

A
  • 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
Q

Why is solid ice less dense than liquid water

A
  • 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
Q

Why does water hae a high melting and boiling point

A
  • 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
Q

What are other anomalous properties of water except for high melting and boiling points and ice being less dense than liquid water

A
  • high surface tension
  • high viscosity
  • not wet allow insects walk on pond surface

Chemistry Module 2 (5 decks)

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