Bonding - explanation

Define cation

positive ion

Define anion

negative ion

Ionic bond

electrostatic attraction between a positively charged cation and a negatively charged anion

Lattice Structure - Ionic Compounds

regular, repeating 3D arrangement of positive and negative ions held together by strong electrostatic forces (ionic bonds).

When, and why, do ionic compounds conduct electricity

Molten/Aqeuous, this is because the positive and negative ions are free to move, allowing them to carry an electric current

Why do ionic substances have high melting points?

Because they have a giant crystal lattice of oppositely charged ions held together by strong electrostatic forces (ionic bonds), which require a lot of energy to break.

Explain why ionic substances are hard and brittle.

Ionic substances are brittle because when a force shifts the layers of ions, like charges (e.g., cation next to cation) can line up. These repel strongly, causing the structure to fracture or shatter instead of bend.

Explain why ionic substances are soluble in polar solvents.

because polar molecules (like water) have partial positive and negative charges that can surround and attract the ions in the crystal lattice.
These attractions can be strong enough to overcome the ionic bonds, causing the lattice to break apart and the ions to dissolve and disperse in solution.

Describe molecules

non-metal atoms held together by covalent bonds.

State the VSEPR Theory

Valence Shell Electron Pair Repulsion Theory

Explain VSEPR Theory

electron pairs in the valence shell of an atom repel each other and will arrange themselves as far apart as possible to minimize repulsion.
This arrangement determines the 3D shape of molecules, considering both bonding electron pairs and lone pairs around the central atom.

What repels more strongly than bond pairs

lone pairs

2 electron pairs & no lone pair

Linear, 180

3 electron pairs & no lone pair

trigonal planar, 120

3 electron pair & one lone pair

bent/angular, 120

4 electron pair & no lone pair

tetrahedral, 109.5

4 electron pair & one lone pair

trigonal pyramidal, 109.5

4 electron pair & two lone pair

bent or angular, 109.5

why do bond angles in molecules arise?

lectron pairs arrange themselves to be as far apart as possible to minimize repulsion

Define electronegativity

a measure of the ability of an atom to attract an electron

How does a difference in electronegativity between two atoms affect their bond?

A difference in electronegativity causes the shared electrons to be pulled closer to the more electronegative atom, resulting in a polar covalent bond with partial charges negative on the more electronegative atom and positive on the other.

What is a bond dipole?

separation of charge within a bond caused by the difference in electronegativity, creating a partial positive and partial negative end.

How does molecular shape affect whether a molecule has a molecular dipole?

If bond dipoles are arranged so they do not cancel out due to the molecule’s shape, the molecule has an overall molecular dipole moment and is polar. If they cancel out, the molecule is nonpolar.

In a non-polar molecule, what are the terminal atoms

all the same

what does polarity depend on

bond and geometry

Why do polar substances dissolve in polar solvents?

because Polar molecules have regions of partial positive and negative charges (dipoles), and these dipoles are attracted to the opposite charges in other polar molecules. This attraction is strong enough to overcome the intermolecular forces holding the solute molecules together, allowing them to separate and mix with the solvent molecules to form a solution. 

Why do non polar substances dissolve in non-polar solvents

the attraction between the substance and the solvent is strong enough to overcome the

solute-solute and solvent-solvent attractions.

Why don’t polar and nonpolar substances usually dissolve in each other?

polar solvents cannot pull apart nonpolar molecules, so they don’t mix well.

What type of bonding holds atoms together within a molecular substance?

Atoms within a molecule are held together by strong covalent bonds.

What holds the molecules together in a molecular substance?

Weak intermolecular forces

Why do molecular substances have low melting and boiling points?

Because the weak intermolecular forces between molecules need to be overcome to melt or boil the substance, less energy is required, resulting in low melting and boiling points.

How do melting and boiling points of molecular substances compare to ionic or metallic substances and why?

much lower melting and boiling points than ionic or metallic substances because ionic and metallic bonds are much stronger than intermolecular forces.

Why do molecular substances generally act as electrical insulators?

Because there are no free-charged particles to carry an electric current

Describe the structure of the metal lattice.

made up of positive metal nuclei (cations) surrounded by a sea of mobile (delocalised) electrons that move freely throughout the lattice. The electrostatic attraction between the positive nuclei and the negative electrons holds the lattice together.

What is the nature of the metallic bond?

electrostatic attraction between positive metal ions (cations) arranged in a lattice and the delocalised sea of mobile electrons that surround them. These free electrons are not bound to any one atom and can move throughout the structure, which holds the metal ions together

How does the structure and bonding within metals allow them to conduct electricity?

Metals have a lattice of positive metal ions surrounded by a sea of delocalised electrons. The metallic bond is formed by non-directional electrostatic forces between these ions and the free electrons. Because these forces are non-directional, the electrons can move freely as free moving charged particles throughout the metal. This movement of electrons allows metals to conduct electricity efficiently.

How does the structure and bonding within metals allow them to be shaped using force?

Metals have a lattice of positive ions surrounded by a sea of delocalised electrons held together by non-directional metallic bonds. Because these bonds are non-directional, the layers of metal ions can slide over each other when force is applied without breaking the bond. The sea of electrons continues to hold the ions together, allowing metals to be malleable and ductile.

Why can most metals be described as ‘hard’ in terms of their structure and bonding?

because their structure consists of positive metal ions in a regular lattice held together by strong non-directional metallic bonds surrounded by a sea of delocalised electrons. These strong electrostatic attractions between ions and electrons make it difficult to move or remove ions from the lattice, giving metals their hardness.

Why do metals have high melting points in terms of their structure and bonding?

Metals have a lattice of positive metal ions surrounded by a sea of delocalised electrons. The strong electrostatic attraction between the positive ions and the mobile electrons forms strong metallic bonds. A large amount of energy is required to overcome these strong bonds and separate the ions, resulting in high melting points.

Why are metals generally insoluble in any solvent in terms of their structure and bonding?

Metals have a strong lattice of positive metal ions held together by non-directional metallic bonds surrounded by a sea of delocalised mobile electrons. This strong bonding throughout the lattice makes it difficult for solvent molecules to break apart the structure. Because solvents cannot easily separate the metal ions, metals are generally insoluble.

What are covalent network substances made from

non-metal atoms covalently bonded in a 2D or 3D network (giant lattice)

Why do covalent network solids have a high melting/boiling point

because they are made of non-metal atoms covalently bonded together in a giant 2D or 3D network. To melt them, many strong covalent bonds throughout the whole structure must be broken. These bonds require a very large amount of energy to overcome, which is why covalent network solids have extremely high melting points.

Why are covalent network substances “hard”

their atoms are bonded together by strong covalent bonds in a giant 3D (or 2D) network. These covalent bonds are very strong and extend throughout the whole structure, so a large amount of force is required to break them. This makes covalent network substances extremely hard.

Electrical Conductivity and Covalent Network Substances

do not conduct electricity because all of their valence electrons are used in covalent bonds, so there are no free or delocalised electrons to carry charge.

Solubilty and Covalent Network Substances

insoluble because their particles are covalently bonded together in a giant network. The attractions between the substance and the solvent are not strong enough to overcome these strong covalent bonds, so the network does not break apart and dissolve.

Malleability and 3D Covalent Network

all atoms are covalently bonded to each other. Applying a force does not cause the atoms to shift because there is not enough energy to break these strong bonds. If the bonds did break, the structure would shatter rather than bend, so these substances are not malleable.

Explain Diamond

3D covalent network in which each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This structure makes diamond very hard, gives it a high melting point, and means it does not conduct electricity because there are no delocalised electrons.

Explain Graphite

layers of carbon atoms arranged in hexagonal sheets, where each carbon is covalently bonded to three others. One electron per carbon atom is delocalised between the layers, and the layers are held together by weak forces, making graphite soft, slippery, and able to conduct electricity along the layers.

Explain SiO2

3-dimensional covalent lattice in which each silicon atom is covalently bonded to four oxygen atoms, forming a strong, rigid lattice. high melting points, hardness, and low electrical conductivity.

Explain SiC

3-dimensional covalent lattice, in which each silicon atom is covalently bonded to four carbon atoms forming a strong, rigid lattice. high melting points, hardness, and low electrical conductivity.

Endothermic Reactions

reaction that absorbs energy from its surroundings. Bonds breaking. Products have more energy than reactants

Exothermic Reactions

reaction that releases energy to its surroundings. Bonds broken. Reactants have more energy than products

Explain activation energy

minimum energy that must be absorbed by the reactants to initiate a chemical reaction

Enthalpy Formula

Bonds broken - bonds formed

State change (endo)

solid > liquid > gas. energy is absorbed from the surroundings to overcome the forces holding particles together.

State change (exo)

gas > liquid > solid. energy is released to the surroundings as particles form stronger bonds and move closer together