Chemical Bonding and Structure Flashcards
Bonding
It refers to the way in which atoms are joined together and combine with one another.
Aim of Bonding
To achieve fully-filled valence electron shells which is very stable just like those of noble gases.
Atom
Smallest particle of an element that has the chemical properties of that element.
Molecule
Two or more atoms covalently bonded together.
Element
Pure substance that cannot be split into two or more simpler substances by physical or chemical processes.
Compound
Substance which contains two or more elements chemically combined in a fixed composition.
Mixture
Two or more substances physically mixed in any proportion.
Differences between compounds and mixtures
- How are they made?
- How are they separated/broken down?
- Are their properties the same as that of their components?
- C: Two or more elements chemically combined in a fixed composition.
- M: Two or more substances physically mixed together in any proportion.
- C: Can only be broken down into its elements or into simpler compounds by chemical processes.
- M: Components of a mixture can be separated by physical means.
- C: Physical and chemical properties of a compound are different from its constituent elements.
- M: The chemical properties of a mixture are the same as those of its components.
Ion
A charged particle either formed by either the gain or loss of electrons.
Anion & Cation
Anion
- Gain es, negative ion
- No. of p < e
- Normally metals
Cation
- Lose es, positive ion
- No. of p > e
- Normally non-metals
Ionic Bonding
- How are these atoms joined together?
- What holds the charged particles together?
- Summarize ionic bonding.
- Atoms are joined together by electron transfer.
- These charged particles are held together by strong electrostatic attraction between oppositely charged ions.
- Essentially complete electron transfer from an element that has high tendency to give away es to an element that has high tendency to take in es.
Electron Transfer
The gain or loss of electrons resulting in the formation of ions.
Ionic Bonds
Strong electrostatic forces of attraction between oppositely charged ions
Ionic Compounds
- Giant ionic (lattice) structure, not just with one cation and one anion
- https://docbrown.info/page04/4_72bond/Image546.gif
Properties of Giant Ionic Structure (5)
MOST UNIQUE PROPERTY: Unable to conduct electricity in solid state, but able to conduct electricity in molten and aqueous state.
- It has giant ionic structure. In solid state, the oppositely charged ions can only vibrate about their fixed positions. Hence, there are no free-moving/mobile ions to conduct electricity.
- In the aqueous/molten state, there are free moving/mobile ions to conduct electricity.
High melting & boiling point. Generally exist as solids at r.t.p. Ionic compounds are hard.
- It has a giant ionic structure. Large amount of energy needed to overcome strong electrostatic forces of attraction/strong ionic bonds between the oppositely-charged ions.
Most ionic compounds are soluble in water. Usually insoluble in organic solvents (eg. ethanol, hexane).
E.g. NaCl / Sodium Chloride
Covalent Bonding
How is it formed?
Covalent bond is formed by the sharing of electrons
Covalent Bonds
Strong electrostatic forces of attraction between the positively-charged nuclei and shared pair of electrons (bonding electrons).
No charged particles formed; only groups of atoms called molecules.
Simple Covalent Structure (2)
- Strong covalent bonds between atoms
- Weak intermolecular (i.e. between molecules) forces of attraction
- Melting/boiling point is low if intermolecular forces of attraction are weak, high if strong
- If intermolecular forces of attraction are broken, the molecules will break apart and move randomly at high speeds.
Properties of Simple Covalent Structure
MOST UNIQUE PROPERTY: Low melting & boiling point. Many substances with simple covalent structures are liquids and gases at r.t.p.
- It consists of small, discrete molecules with a
simple covalent structure. Only a small amount of energy needed to overcome the weak intermolecular forces of attraction
- Note: Strong covalent bonds between atoms are not broken (eg. water does not change chemically when boiled) during changes of state.
Generally unable to conduct electricity in any state.
- It consists of small, discrete molecules with a
simple covalent structure. There are no mobile/free-moving ions or delocalised electrons to conduct electricity.
Most molecules with simple covalent structures are insoluble in water.
- Some exceptions: ammonia, hydrogen chloride, sulfur dioxide (refer to Experimental Chemistry notes)
- Usually soluble in organic solvents (eg. ethanol, hexane).
E.g. CO2 / Carbon dioxide, H2 / Hydrogen molecule, N2 Nitrogen molecule, CH4 / Methane etc.
Giant Covalent Structure
ONLY COVERING DIAMOND AND GRAPHITE.
- Diamond and graphite are allotropes of carbon, which are different forms of an element
- Diamond and graphite are examples of substances having giant covalent structures
Giant Covalent Structure
(Diamond)
Each carbon atom is covalently bonded to 4 other carbon atoms in a repeated tetrahedral arrangement.
Giant Covalent Structure
(Graphite)
- Each carbon atom is covalently bonded to 3 other carbon atoms in a repeated hexagonal arrangement. They form parallel layers of carbon atoms, which are held by weak intermolecular forces of attraction.
- Since only 3 out of 4 valence electrons of each carbon atom are involved in covalent bonding, the fourth valence electron is not used in bonding, and is delocalised and able to conduct electricity.
Properties of Giant Covalent Structure
MOST UNIQUE PROPERTY: Very high melting and boiling point.
- It has a giant covalent structure. Large amount of energy needed to overcome strong covalent bonds between carbon atoms.
Diamond is unable to conduct electricity. Graphite is able to conduct electricity.
- Diamond has a giant covalent structure. Each carbon atom uses up all four of its valence electrons to form covalent bonds with four other carbon atoms.
- It does not have any delocalised electrons to conduct electricity.
- Graphite has a giant covalent structure. Each carbon atom uses 3 out of 4 of its valence electrons to form covalent bonds with 3 other carbon atoms.
- Each carbon atom has one valence electron not used in bonding; it is delocalised and is able to conduct electricity.
Diamond is very hard. Used as a cutting tool or drill bit to cut hard objects like glass and rocks. Graphite is soft and slippery. Used as a lubricant and in pencil lead.
- Diamond has a giant covalent structure, large amount of energy needed to overcome strong covalent bonds between carbon atoms.
- Graphite has a giant covalent structure, is soft and slippery because the layers of carbon atoms are held by weak intermolecular forces and can slide over each other easily.
Insoluble in water and organic solvents.
Metallic Bonds
Strong electrostatic forces of attraction between metallic cations and ‘sea’ of delocalised electrons.
