SC6 Covalent Bonding
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What is a covalent bond?
A shared pair of electrons between two non-metals in their outermost shell
Define molecule
Consists of a group of two or more atoms joined together by covalent bonds
What type of diagram can be used to represent a 2d model of a covalently bonded substance?
Dot and cross diagrams
State some examples of common molecular elements
• oxygen • hydrogen • nitrogen • fluorine • bromine
State some examples of common molecular compounds
• ammonia • methane • carbon dioxide • nitrogen monoxide • ethane
What is the approximate size of atoms and small molecules?
• Atoms are smaller than molecules • molecules are around 0.1nm across
Describe the dot and cross diagram for the formation of a simple molecule
• outer shell of each atom is drawn as a circle • circles overlap where there is a covalent bond • electrons from one atom are drawn as dots and from the other as crosses • no inner shells drawn
Describe how a simple molecule can be modelled by drawing its structure
• show each atom using its element symbol • show each covalent bond as a straight line
What is the state of molecular substances at room temperature?
Gaseous or Liquid
What are intermolecular forces?
Forces of attraction between molecules
What are the physical properties of molecular substances?
• low melting and boiling point • no conductivity • tend to be soft and flexible • tend to be more flammable than ionic substances
Why do molecular substances have low melting and boiling points?
• the weak intermolecular forces are easily overcome
Why doesn’t the molecule break apart if it has low melting and boiling points?
The actual covalent bonds aren’t overcome and therefore the actual particle itself doesn’t get undone
Why can’t molecules conduct electricity?
Simple molecules have no overall charge so they can’t conduct electricity
Why are molecules more flammable than ionic substances?
Many flammable substances contain hydrogen and carbon, both of which are common in many molecular compounds
What are intramolecular forces?
Forces that bind together the atoms whichare between the subatomic particles of the atoms itself.