Flashcards in Chemical bonding Deck (37)
What is ionic bonding?
The bond formed from the electrostatic attraction between two oppositely charged ions; usually between a metal and a non-metal but can be between ionic compounds (non-metals) and non-metals.
How do cations form?
When a metal atom loses all of its valent electrons to have a full outer shell, leaving the net charge of the atom positive.
How do anions form?
When a non-metal gains electrons in its valent shell to form a full outer shell, leaving the net charge negative.
How can you work out ionic charge from the periodic table?
- Group 1-3 elements usually form cations with a charge in accordance with their group number.- Group 5-7 elements usually form anions with a charge of 8-n (n being the group number).- Group 0 elements do not usually react at all as they are very stable.- Group 4 ions don't usually form ions as too much energy is required to transfer electrons between them.- The transition metals can usually form more than one ions. Their oxidation state will determine their ionic charge.
How do ionic compounds form solids?
They form 'Giant ionic lattices'. These lattices consist of billions of ions packed in a regular repeating pattern. They are packed in a way so that each ion is surrounded by the maximum number of oppositely charged ions but is as far away from ions of the same charge as possible.
What does 'giant' imply in this context?
Giant describes a structure that does not have a definite end/ has the potential to reach an infinite size provided with an infinite number of components. There isn't a formula to describe the exact size of the structure, only simple ratios. For example, water is a molecule with a definite size, but Sodium Chloride crystals can be of any size.
What are the typical physical properties of ionic compounds?
1. High melting and boiling points.2. Don't conduct electricity when solid but do when liquid or in solution.3. Ofter soluble in water.4. Brittle.
Why do giant ionic lattices have high melting and boiling points?
The electrostatic force of attraction between the anions and cations are strong and many in an ionic lattice, so a lot of heat energy is required to break them; so ionic lattices have high melting and boiling points.
Why do giant ionic lattices conduct as liquids and in solution but not when solid?
As a solid, all ions are held tightly in place and there are no free electrons or charge carriers, so an electric current cannot pass through the solid. However, as a liquid or in solution, the ions are free to move around. During electrolysis, cations move towards the cathode and gain electrons to form elements; the anions lose electrons at the anode. This process maintains a potential difference so a current can flow.
Why do ionic compounds dissolve in water?
The ions are attracted to the polar water molecules. If that attraction is strong enough to break the ionic bonds between the ions, then the compound dissolves in water.
Why are giant ionic lattices brittle?
When stress is applied to an ionic crystal, the rows of ions within the crystals shift and try to slide across each other. However, this brings ions of the same charge side by side and they repel each other, so cracks form along the contours of the rows of ions. This makes ionic crystals brittle.
What is covalent bonding?
A bond formed when pairs of electrons are shared between atoms to achieve full outer shells.
How do you determine the number of bonds an element can form from the periodic table?
- Hydrogen usually forms 1 covalent bond.- Group 4-7 elements usually form 8-n (n being the group number) covalent bonds but can vary depending on context.
Are there exceptions to the rule?
Sometimes a compound is more stable when an element in that compound does not achieve a full outer shell. This is the case with boron in boron trichloride when the boron only has 6 electrons in the outer shell and sulfur in sulfur hexafluoride when the sulfur has 12 electrons in its outer shell.The boron is described as electron deficient and the sulfur is described as having an expanded octet.
Rules for exceptions to the octet rule.
1. The maximum number of covalent bonds that can be formed by an element is equal to the number of electrons in the outer shell.2. Expanded octets can only be formed with elements of the 3rd period or above as they have d shells.
What is a dative covalent bond?
When the bonding pair of electrons in a covalent bond is provided by only one of the atoms in the bond.
What is a simple covalent molecule?
Elements bonded by covalent bonds in molecules.
What are the properties of simple covalent molecules?
1. Low melting and boiling points. Intermolecular forces are weak and do not require a lot of heat energy to break.2. Do not conduct electricity. Electrons are not free to move and carry a current.3. Soluble in organic solvents. Intermolecular forces are weak and easily broken by attraction to solvent molecules.
What is a giant covalent lattice?
Three dimensional lattice structure consisting of atoms held together by strong covalent bonds.
What are the properties of giant covalent lattices?
1. High melting and boiling points. Covalent bonds are strong and require lots of energy to break.2. Do not conduct electricity (except graphite). No free moving charge carriers to carry an electric current except for graphite who has one free electron per atom to carry electric current.3. Insoluble in organic solvents. Covalent bonds are too strong to be broken by the attraction to solvent molecules.
What is the structure and physical properties of diamond?
1. Diamond has a tetrahedral structure. Each atom of carbon makes 4 bonds to 4 other carbon atoms.2. Does not conduct electricity. No free moving charge carriers within the structure as all electrons are used for bonding.3. Hard. The tetrahedral structure of diamond distributes force applied to the structure evenly across the whole structure. There are no weak points, making diamond very hard.
What is the structure and physical properties of graphite?
1. Graphite has a layered hexagonal structure. Each carbon makes 3 bonds to 3 other atoms to form a two dimensional hexagonal structure. The layers are then stacked on top of each other to form the final three dimensional structure.2. Does conduct electricity. Each carbon atom only makes 3 bonds so only 3 electrons are used. The 4th electron is free to jump between the carbon atoms in the same plane and layer. This means that they are able to carry an electric current through the structure and so graphite does conduct electricity.3. Soft. The forces holding each layer together within the graphite crystal are relatively weakly bonded together with Van Der Waal's interactions. They slide past each other relatively easily. This allows for graphite to be used as quite an effective lubricant.
What is metallic bonding?
The electrostatic force of attraction between a positive metallic cation and the surrounding sea of delocalised electrons.
What are the properties of a metallic crystal?
1. Metallic crystals have high melting and boiling points. The metallic cations are fixed in place by the strong electrostatic force between them and the delocalised electrons. It takes a lot of heat energy to break that force of attraction and break apart the metallic lattice, so metals usually have fairly high melting and boiling points.2. Good conductors of electricity. The electrons in the sea of delocalised electrons are non-specific to a metallic cation and are free to jump between any cation. This ability means that when a potential difference is applied, the electrons in the sea of electrons are free to move in any direction to carry the current.3. Insoluble. Metallic bonds are too strong to be broken by attraction of cations in the lattice to solvent molecules.4. Malleable and ductile. Metallic bonds are non-directional, so will hold no matter what position metallic cations are in. This allows the layers in the metallic lattice to slide past each other easily. When the positive cations are side by side, the sea of electrons also act as shielding to prevent them from repelling each other. This results in metal having the ability to change shape easily and being ductile and malleable.
What does VSEPR theory state?
1. Electron pairs in the outer shell are all negatively charged and thus will repel each other as far away from each other as possible.2. Lone pairs of electrons have a greater repulsion than bonded pairs.
How do we determine the shape of a simple molecule?
1. Draw a dot-to-cross diagram of the molecule.2. Count the number of lone pairs around the central atom to determine the shape.3. Account for any lone pairs in the process.4. Draw the three dimensional structure of the molecule.
What are the corresponding shapes to the number of valent shell electron pairs?
- 2 pairs correspond to a linear shape. Bonding angle: 180 degrees.- 3 pairs correspond to a trigonal plainer shape. Bonding angle: 120 degrees.- 4 pairs correspond to a tetrahedral shape. Bond angle: 109.5 degrees.- 6 pairs correspond to a octahedral shape. Bond angle: 90 degrees.
What happens when lone pairs are involved?
Each lone pair reduces the bond angle by 2.5 degrees.
What are Van der Waal's interactions?
The attraction between the induced dipoles of neighbouring molecules.