bonding Flashcards by i <3

what is ionic bonding

electrostatic force of attraction between oppositely charged ions formed by electron transfer

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what do square brackets tell us
[Na]+

charge is spread over whole ion

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what are electrostatic forces of attraction in an ionic lattice

ions in lattice are attracted to every other oppositely charged ion

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physical properties of ionic compounds

high melting and boiling point - due to large amount of energy to overcome strong electrostatic forces of attraction
soluble in polar solvents - soluble substance e.g water, surrounds the ions and overcome electrostatic forces between the ions
(if charge of ions increase, solubility decreases as water cannot overcome the electrostatic forces of attraction)

3.do NOT conduct electricity when solid - ions locked in place by electrostatic forces of attraction and cant carry a charge
dissolved in water + conducts electricity as they’re free to move

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ionic compounds examples

sodium chloride NaCl

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what is covalent bonding

between two non-metals
electrons are shared between two outer shells to achieve a full outer shell (same electron configuration of a noble gas)

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what are the pair of electrons attracted to in covalent bonding

the two nuclei of atoms forming the bond

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what does the line represent in covalent bonds
H—–H

shared pair of electrons

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what is dative covalent bonding/ coordinate bonding

when at atom uses a lone pair of electrons to form a covalent bond
(both electrons in shared pair are supplied from a single atom)

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what is a lone pair

electrons that are not shared with another atom

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for a dative bond to form, what must the acceptor atom be

electron deficient (available orbitals for electrons to occupy)

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what is average bond enthalpy

tells us the strength of the bond

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what do the solid lines tell us on shapes of molecule

that two bonds and atoms attached lie on the plane of the screen/page

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what does a solid wedge tell us on shapes of molecule

bond is coming out of plane of page

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what do the dotted wedge tell us on shape of molecules

bond is projected back behind plane of page

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what is electron pair repulsion theory

shape of molecule is determined by the electron pairs surrounding the central atom (referring to outer shell)
electrons repel all of other electron pairs
electrons move as far apart as possible to minimise repulsion

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what molecule has bond angle 180

linear
e.g beryllium chloride
Cl – Be – Cl

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which molecule has bond angle 104.5

v - shaped or non linear
e.g H2O

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which molecule has bond angle 120

trigonal planar
e.g BF3

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which molecule has bond angle 107

triangular pyramid
e.g NH3

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which molecule has bond angle 109.5

tetrahedral
e.g CH4 methane / NH3 ammonium

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which molecule has bond angle 90 AND 120

trigonal bipyramid
e.g PCl5

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which molecule has bond angle 90

octahedral
e.g SF6

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for every lone pair present, what happens to the bond angle between covalent bonds

reduced by 2.5 degrees

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how are dative bonds presented

indicated using an arrow from lone electron pair H | H ---- N ➜ H | H

why do lone pairs reduce bond angle by 2.5 degrees

repel more strongly than bonding pairs

define electronegativity

ability of an atom to attract a pair of electrons in a covalent bond

what happens to electronegativity ALONG a PERIOD

increases

what does the power of electronegativity depend on

1. size of positive charge on nucleus (more protons = increased positive charge ➜ increases attraction between nucleus and pair of electrons in covalent bond 2. atomic radius (smaller atomic radius = closer bonding electrons to nucleus ) L➜R (periodic table) atomic radius decreases 3. shielding of nucleus of nucleus by electrons in inner shells (more inner shells + lower electronegativity)

what happens to electronegativity DOWN a GROUP

decreases

what are some of most electronegative elements

fluorine oxygen nitrogen chlorine

whats a dipole

a separation of charge

are elements on right or left of periodic table more electronegative

right

whats a pure covalent bond

has no dipole

how to show that a bond is polar

write delta positive (δ+) and delta negative (δ-) to show charges

what does delta δ show

shows that the charge is small as the electron pair has shifted towards the MORE electronegative atom

where does the delta negative δ- go

goes on more electronegative element

name the 3 intermolecular forces

1. van de waals forces (induced dipole) 2. permanent dipole 3. hydrogen bonding

whats a polar bond

bonding of two atoms with different electronegativites

what are simple molecular substances

substances with small molecules each molecule has fixed number of atoms

where do intermolecular forces take place

in-between molecules

intermolecular forces properties

weaker than covalent bonds easily broken by high temp

what happens when intermolecular forces are heated

molecules move faster intermolecular forces break at a certain temp causes molecules to move away from each other

why do intermolecular forces have low boiling point

small amount of energy to break intermolecular forces

what are induced dipole-dipole interactions (van de waals)

- weakest type of intermolecular force - caused by random electron movement - acts as an induced dipole between molecules

what does strength of van de waals depend on

depends on number of electrons (larger amount of electrons = higher boiling point - experience stronger van de waals)

what are permanent dipole-dipole interactions

when permanent dipoles leads to attraction acts between polar molecules δ+ and δ- attract each other hold molecules together in lattice-like structure

what is the strongest type of intermolecular force

hydrogen bonding

what is the weakest type of intermolecular force

van de waals

where do hydrogen bonds only form between

between 3 most electronegative atoms: nitrogen oxygen fluorine | (all have at least one lone pair of electrons)

what two conditions are needed for hydrogen bonding to take place

1. hydrogen atom bonded to strong electronegative element 2. electronegative atom must have at least one lone pair of electrons

what is hydrogen bonding

type of permanent dipole dipole bond strongest intermolecular forces between neutral molecules act between molecules containing permanent dipoles

where does hydrogen bonding take place

in compounds that have a hydrogen atom attached to one of the three most electronegative atoms

why does water have a high melting and boiling point

it takes a great deal of energy to break the hydrogen bonds

properties of after due to hydrogen bonding

ice is less dense of liquid form therefore ice floats on water liquid water = water molecules moving randomly freezing point = water molecules in ordered structure = ice - stabilised by hydrogen bonds (in ice - water molecules are further apart than in liquid water making it less dense & floats)

what bond is between atoms of simple molecular substances

covalent

what do simple molecular substances have

small molecules with fixed number of atoms

2 examples of giant covalent structures

diamond and graphite

properties of simple molecular substances

low melting and boiling points due to weak intermolecular forces

what happens when you cool a simple molecular substance below its melting point

becomes a solid simple molecular lattice

molecule of iodine

consists of two iodine atoms joined by a single covalent bond with intermolecular forces between the molecules

what are non-polar molecules

atoms that have same electronegativity means that only van de waals can act between the molecules

what the solubility of simple molecular substance depend on

depends on whether the substance is polar or none polar

iodine solubility

solid at room temp iodine molecules held in simple molecular lattice by van de waals

what happens when non polar substances e.g iodine dissolve in non polar substances

solvent molecules form van de waals to iodine molecules

why are non polar substances insoluble in polar e.g water solvents

molecules with hydrogen bond remain hydrogen bonded rather than forming van de waals with non polar molecules

general rule of polar substances

polar substances dissolve in polar solvents

what dont simple molecular substances contain

mobile charged particles (means that simple molecular substances cant conduct electricity)