chemical bonding & structures Flashcards
1
Q
Definition of ionic bonds
A
Ionic bonds are strong electrostatic forces of attraction between oppositely changed ions, metals and non metals
2
Q
Structure of ionic compounds
A
- In the solid state, the actual structure consists of a continuously repeating three-dimensional lattice with an uncountable large number of formula unit of positive and negative ions
- ions are closely packed, arranged in an orderly manner and held in fixed positions by strong elect static forces of attraction between oppositely-changed ions
- the structure formed by ionic compounds is known as giant ionic structure
- the electrostatic attraction of each ion affects all the other ions around it. It acts equally in all directions
3
Q
Structure of sodium chloride
A
- Sodium chloride has a giant ionic structure
- in the structure of sodium chloride, the ratio of sodium ions to chloride ions is 1 : 1
- each sodium ion is surrounded by 6 chloride ions
- Each chloride ion is surrounded by 6 sodium ions
4
Q
Physical properties of ionic compounds - high melting point
A
- Ionic compounds generally have high melting points
- they generally exist as solid at room temperature and pressure
- explanation: ionic compounds, such as sodium chloride, have giant ionic structure. Large amount of energy is required to overcome the strong electrostatic forces of attraction between oppositely-changed ions
5
Q
Physical properties of ionic compounds - conductor of electricity in molten and aqueous states
A
- In the solid state, ionic compounds cannot conduct electricity
- ionic compound conduct electricity only when in molten state or aqueous state
- molten hate is a state when a solid substance has melted. Aqueous state to a state when a substance has dissolved in water
- explanation: ionic compounds, such as sodium chloride, have giant ionic structure.in the solid state, the oppositely charged ions are held in a fixed position by strong electrostatic forces of attraction between oppositely-changed ions. Thus, ions are not free-moving and hence cannot conduct electricity.in the molten or aqueous state, the strong electrostatic forces of attraction between oppositely changed ions have been overcome. The ions are free-moving and hence can conduct electricity.
6
Q
Physical properties of ionic compounds - soluble in water but insoluble in organic solvent
A
- Ionic compounds are generally soluble in water but insoluble in organic solvent.
- examples of organic solvent are ethanol, trichloromethane, turpentine, and benzene
- examples of ionic compounds that and insoluble in water: silver chloride, barium sulfate
7
Q
Uses of ionic compounds - high melting point
A
- Used as refractory materials
- refracting materials are heat resistant , the melting point of magnesium oxide in 2852°C. It is used to line the inner surface of a high temperature furnace
8
Q
Covalent bonding
A
- covalent bonds are generally formed between non-metal atoms by the sharing of electrons
9
Q
Electronegativity
A
- Electronegativity refers to the ability of an atom to attract a shared pair of electrons towards itself in a covalent bond
- electronegativity increases across a period
- electronegativity decreases down a group
- fluorine is the most electronegative atom
10
Q
Non-polar and polar covalent bonds
A
- if the two atoms involved in covalent bond are either the same or have similar electronegativity, a non-polar covalent bond results. The two atoms have equal pull on the shared pair of electrons.
-If the two atoms involved in covalent bonding have different electronegativity values, the pair of shared electrons are not equally shared between the two atoms and polar covalent bond results ( if atom B is more electronegative than A,the bonding electrons are nearer to B in the bond ) - in a polar covalent bond, the more electronegative atom acquires a partial negative charge and the less electronegative a tem acquires a partial positive charge
11
Q
Structure of simple molecular substances
A
- Simple molecular substances consist of many simple molecules
- within each molecule, the atoms are held together by strong covalent bonds
- however, the molecules are held together by weak intermolecular forces of attraction
- the structure of simple molecular substances is known as simple molecular structure
- examples: water, methane, carbon dioxide, ammonia, iodine.
12
Q
Properties of simple molecular substances - low melting point and boiling point
A
- Simple molecular substances generally have low melting point and boiling point
- they generally exist as liquids or gases at room temperature
- explanation: methane example. Methane has a simple molecular structure. Small amount of energy is required to overcome the weak intermolecular forces of attraction. Therefore, methane has a low melting and boiling point
13
Q
Properties of simple molecular structure - non-conductor of electricity in any state
A
- Simple molecular substances generally do not conduct electricity in any state
- Explanation: using methane. Methane has a simple molecular structure. There are no free moving valence electrons available to conduct electricity
14
Q
Properties of simple molecular structure - insoluble in water but soluble in organic solvents
A
- Simple molecular substances are generally insoluble in water but soluble in organic solvents
15
Q
Uses of simple molecular substances
A
Volatile - uses in perfume and flavorings, in room deodorants, insect repellents
16
Q
Structure of giant molecular substances
A
- Besides forming simple molecules, atoms can form a network of strong covalent bonds throughout the structure
- this will result in the formation of a giant molecular structure
- examples: diamond, graphite, silicon dioxide
17
Q
Allotropes of Carbon
A
- Allotropes are different forms of the same element. Allotropes may have different properties such as hardness and electrical conductivity
- two well-known allotropes of carbon are diamond and graphite
18
Q
Structure of diamond
A
- diamond has a giant molecular structure
- in the structure of diamond, each Carbon atom is covalently bonded to four other Carbon atoms in a tetrahedral arrangement
19
Q
Properties of diamond - high melting point
A
- Diamond has very high melting point, about 3550°C
- explanation: diamond has a giant molecular structure. A large amount of energy is required to break strong covalent bonds between carbon atoms, therefore, diamond has a high melting point
20
Q
Properties of diamond - diamond does not conduct electricity
A
- Explanation: diamond has a giant molecular structure. All the four valence electrons of each carbon atom are used for covalent bonding, so there are no free-moving valence electrons present to conduct electricity
21
Q
Properties of diamond - solubility (in water and organic solvents)
A
- Diamond is insoluble in water and organic solvents
22
Q
Properties of diamond - diamond is hard
A
- All the carbon atoms are hold by strong covalent bonds throughout the structure, hence diamond is hard
- due to its hardness, diamond is often used as drill tips and polishing tools
23
Q
Uses of diamond
A
- hard: tips of cutting, grinding, and polishing tools
24
Q
Structure of graphite
A
- Graphite has a giant molecular layered structure
- graphite is made up of many layers of hexagonal rings of carbon atoms
- each carbon atom forms strong covalent bonds with three other carbon atoms, in hexagonal arrangement in layers
- the carbon atoms are held together by strong covalent bonds but the layers are held together by weak intermolecular forces of attraction
25
Q
Properties of graphite - graphite has high melting point
A
- Graphite has very melting point, about 3650°C
- explanation: graphite has a giant molecular layered structure. A large amount of energy is required to break the strong covalent bonds between the carbon atoms. Therefore, graphite has a high melting point.
26
Q
Properties of graphite - graphite can conduct electricity
A
- Explanation: each carbon atom uses only three out of four valence electrons in bonding. The valence electrons not used in bonding are free-moving to conduct electricity
27
Q
Properties of graphite - solubility of graphite
A
- Graphite is insoluble in water and organic solvents
28
Q
Properties of graphite - graphite is soft and slippery
A
- Graphite has a giant molecular layered structure
- the layers of carbon atoms in graphite are held together by weak intermolecular forces of attraction. The layers of atoms are able to slide over one another when a force is applied
29
Q
Uses of graphite
A
- Soft and slippery: in pencil lead. Since it is soft, the layers of carbon atoms slide off the pencil onto the paper easily. As a soft lubricant to reduce friction in machinery.
- conductor of electricity: in brushes for electric motors and as inert electrodes
30
Q
Structure of silicon
A
- Giant molecular structure
- high melting point
- non-conductor of electricity
- hard solid
- insoluble in water and organic solvent
31
Q
Structure of silicon dioxide
A
- Giant molecular structure
- high melting point
- non-conductor of electricity
- hard solid
- insoluble in water and organic solvent
32
Q
Structure of macromolecules
A
- Covalent substance
- polymers are a class of substances that can be classified as macromolecules
- a polymer or macromolecule consists of many simple covalent molecules or simple molecular substances joined together into chains of much larger molecules (strong covalent bonds between non-metal atoms within each large molecule )
- examples (natural): silk, wool, starch, rubber
- examples (man-made): poly, nylon, polyester
- the huge variety of polymers result in a wide range of physical properties such as hardness and flexibility, allowing them to be made into many different products
33
Q
Properties of polymer/macromolecules - melting and boiling point
A
- Most macromolecules are solid at room temperature and pressure due to their large molecule size, weak intermolecular forces of attraction are strong enough for it to be solid at rtp
- due to the range of sizes of macromolecules, they do not have a fixed melting or boiling point
- instead, they typically soften over a range of low temperatures when heated as the weak intermolecular forces of attraction between the large molecules are overcome by molecular vibrations with higher kinetic energy
34
Q
Properties of polymer/macromolecules - solubility
A
- Most macromolecules are insoluble in water but soluble in organic solvents
35
Q
Properties of polymer/macromolecules - electrical conductivity
A
- most macromolecules are not able to conduct electricity in any states as they do not have mobile ions or electrons
36
Q
Structure of pure metals
A
- In any pure metal, metal atoms are closely packed together in the solid state to form giant metallic structure
- all metal atoms are of the same size and regularly arranged in layers within the metallic lattice.
- the metal atoms in the giant metallic structure lose their valence electrons to become positive ions
- the valence elections are delocalised and can move freely between the metal ions resulting in a ‘sea’ of free-moving valence elections
- metallic bond is the strong electrostatic forces of attraction between the positive metal ions and the ‘sea’ of free-moving valence electrons
37
Q
Structure of alloys
A
- Alloys are a type of solid-solid mixture with one or more other elements
- In alloys, the regular arrangement of metal atoms is disrupted by the addition of other elements with atoms of different sizes which are randomly distributed
- this disrupts the orderly arrangement of atoms in pure metals and hence there is a difference in properties between alloys and pure metal
38
Q
Properties of metals and alloys - metals have high melting point
A
- most metals have high melting point
- explanation: metal has a giant metallic structure. A large amount of energy is needed to overcome the strong electrostatic forces of attraction between the positive metal ions and the ‘sea’ of free-moving valence electrons (exception: mercury)
- alloys melt over a range of temperatures
39
Q
Properties of metals and alloys - pure metals and alloys can conduct electricity in all states
A
- Explanation: Metal has a giant metallic structure. There is a ‘sea’ of free-moving valence electrons present to conduct electricity.
40
Q
Properties of metals and alloys - solubility of metals and alloys
A
- Metals and alloys are insoluble in water and organic solvents
41
Q
Properties of metals and alloys - ductility and malleability
A
- Ductile: metals can be stretched into wires without breaking
- malleable: metals can be hammered into different shapes
- pure metals are ductile and malleable while alloys are harder and stronger
42
Q
Explanation for why pure metals are malleable and ductile
A
- Metals have giant metallic structure
- metal ions are arranged regularly. When a force is applied, the layer of metal ions can slide over one another easily. Therefore, metals are malleable and ductile
43
Q
Explanation for why alloys are harder and stronger than pure metals
A
- In an alloy, the metal atoms and atoms of the added element are of different sizes
- as this disrupts the orderly arrangement of atoms in pure metals, it is much harder for the atoms to slide over each other when a force is applied.
- hence, alloys are harder and stronger than the pure metals they are made from, they tend to be less malleable and ductile
44
Q
uses of metals and alloys
A
- metals are good conductor of electricity, ductile: metals are used in electric wires and in electric goods. the most common metal used is copper.
- high melting and boiling points of metals: tungsten metal has a high melting point of 3410°C. it is used to make the filaments of light bulbs.
- increased hardness and strength of alloys: bronze and brass alloys are used in making more durable items (eg bells). steel is used to make items that can withstand heavy loads (eg warehouse shelves).
