Chapter 4: Chemical Bonding Flashcards
How are noble gases stable?
Each noble gas has a full valence shell. As such, the noble gases are very stable.
Helium gases are stable because…
- Helium has only 1 electron shell which is filled with two electrons. (***)
- Thus, helium has a valence shell.
-Helium has a duplet configuration.
Other noble gas atoms are stable because…
- Atoms of other noble gases have 8 valence electrons.
- Thus, they have a full valence shell.
- This is called an octet configuration.
How do atoms become stable?
An atom is stable if it has duplet or octet configuration. Hence, atoms will try to adopt such configurations by:
- losing or gaining electrons
- sharing electrons
This results in atoms chemically combining with one another (chemical bonds are formed).
Such configurations/structure are also known as a noble gas configurations/structure.
- Positive ions are formed when atoms lose electron(s).
- Negative ions are formed when atoms gain electron(s).
What atoms form cations or anions?
- Atoms of metal form cations (positive ions).
- Atoms of non-metal form anions (negative ions).
When does ionic bonding occur and what is it resulted from?
Ionic bonding occurs when electrons are transferred from one atom to another, forming two oppositely-charged ions.
Ionic bonding results from the strong electrostatic force of attraction (ionic bond) between the positive and negative ions.
Ionic bonding - Occurs between metal and non-metal and involves electron transfer.
How to represent ionic bonding?
Dot and Cross diagram
- Dot represents the molecules of an atom in an element, while cross represents the molecules of an atom in another element.
What forms an ionic structure and what is an ionic compound?
Ionic structures:
- A cation and an anion in an ionic compound will continue to attract other anions and cations.
- The alternating cations and anions form a 3-dimensional structure called a giant ionic crystal lattice.
Ionic compunds:
- An ionic compound is an electrically neutral compound. Hence, the total positive charge from the positive ions must be equal to the total negative charge from the negative ions.
- From the ratio of the ions in the ionic compound, we can determine the formula for the compound.
- For example,
Sodium and chlorine will pair off in a 1:1 ratio. Therefore, the formula of sodium chloride is NaCl.
Structure of sodium chloride:
- Each chloride ion is surrounded by six sodium ions
- Each sodium ion is surrounded by six chloride ions.
The ratio of sodium ions to chloride ions is 1:1. Hence, the formula unit of sodium chloride is NaCl.
What is a covalent bond?
Covalent bonds are formed between atoms of non-metals.
Valence electrons are shared between two atoms.
A covalent bond is the bond formed by the sharing of electrons between two atoms.
Each atom in the molecule achieves a stable noble gas structure.
What are covalent molecules and how is it formed?
Covalent bonds can be formed between
- atoms of the same element;
- atoms of different elements.
A molecule is formed when a group of two or more atoms are held together by covalent bonds.
How are covalent bonds formed?
It is formed by sharing electrons.
A single covalent bond is formed by sharing a pair of electrons, forming a duplet or an octet configuration.
What are covalent substances made up of?
Simple molecules:
- Covalent substances are mostly made up of simple molecules. Simple molecules have countable number of atoms in a fixed ratio.
- Water and wax are both covalent substances made up of simple molecules.
Giant molecules:
- Some covalent substances consist of a giant network atoms that are covalently bonded.
- A giant molecule has a practically uncountable number of atoms.
- Such substances have a giant molecular structures.
- Examples of substances with giant molecular structures: diamond, graphite and silicon dioxide.
What is metallic bonding?
Chemical bond found in metals:
- The particles in metals are held strongly to each other by metallic bonding to form a giant metallic lattice structure.
- In the metal lattice, metal atoms lose their valence electrons and become positively-charged ions.
- These electrons no longer belong to any metal atom and are said to be delocalised.
- The delocalised electrons move freely around the metal ions.
A metallic bond is the electrostatic force of attraction between the positively-charged ions and the ‘sea of mobile delocalised electrons’.
