5) Chemical bonding Flashcards
MODULE 1
Atoms can obtain noble gas configurations by
Ionic bonding or covalent bonding
Ionic bonding
(Chemical bonding) Outright transfer of electrons from one atom to another to form ions
Bonding consists of an electrostatic attraction between the positive and negative ions formed by this transfer of electrons
Covalent bonding
(Chemical bonding) Sharing electrons between adjacent atoms - each atom ‘owns’ all shared electrons
Stable electron configurations
All orbitals (energy levels) are full
Empirical formulae
Chemical formula of a compound that gives the ratios of the elements present
What formulae are always used for ionic compounds
Empirical formulae
Valence (valency)
Number that measures combining power of an element when it forms compounds
Binary compounds & how they are named
(Contains only two elements)
- Give positive ion first, then negative
- Positive ion has same name as the element while the negative ion changes end to ‘ide’
Polyatomic ions
Covalent bonded set of two or more atoms
Covalent bonds
Bonds formed between pairs of atoms by the shared electrons
Electron-dot structures
(Diagrams) formulae of elements/compounds with valence electrons shown as dots
What do electron-dot structures commonly describe
Covalent bonding
Structural formulae & what it is used for
Symbols for atoms connected by short lines that represent chemical bonds—one, two, or three lines standing for single, double, or triple bonds
Identifies location of chemical bonds between atoms of a molecule
Covalent molecular substances
Elements or compounds made up of simple covalent molecules
Molecular formula
Formula for covalent molecular substances and shows number of atom types in a molecule of the substance
When does covalent bonding occur
When BOTH of the elements forming the compound need to gain electrons to attain noble gas configurations
What elements in the periodic table tend to form covalent bonds
Elements in the centre and to the right of the periodic table - elements such as carbon, silicon, phosphorus, oxygen. Some, like oxygen, can also form ionic bonds)
What is the number of covalent bonds an atom forms equal to
Number of electrons the atom needs to gain to acquire a noble gas configuration
If a compound can be ionic / covalent, how would you know its IONIC
- One atom must have a stronger attraction for electrons than the other
- Difference in electronegativities must be greater than 1.5
If a compound can be ionic / covalent, how would you know its COVALENT
- Atoms have similar attractions for electrons, they are more likely to share electrons
- Difference in electronegativities must be smaller than 1.5
What is the best giude to working out whether a compound is ionic or covalent (COMPARING)
Determine
1. One element needs to gain electrons and other needs to lose them (ionic)
2. Both elements need to gain electrons (covalent)
Properties of ionic substances (5)
- Solids at room temp
- High mp & bp
- Hard and brittle
- As solids, do not conduct electricity
- In aqueous solution, do conduct electricity
Properties of covalent substances
- Generally gases or liquids at room temp
- Low mp & bp
- When solid, are soft
- Pure covalent substances do not conduct electricity as solids or liquids
- Don’t conduct electricity in aqueous solution (unless reacting with water)
Metallic structure or metallic bonding
Orderly three-dimensional array of positive ions held together by a mobile ‘sea’ of delocalised electrons
