Particles Of Which Substances Are Made Flashcards
What kind of structure does an ionic substance form?
An ionic crystal lattice
What is an ionic crystal lattice?
A giant 3D structure consisting of billions of ions
What kind of force holds an ionic crystal lattice together?
Electrostatic force
What is an electrostatic force?
The force of attraction between negative and positive ions
What is the magnitude of an electrostatic force?
It is very strong
What phase are ionic compounds at room temperature?
Solids
What kind of melting point does an ionic compound have?
High
Why do ionic compounds have high melting points?
It takes a lot of energy to overcome the electrostatic forces holding the solid together
Can ionic compounds conduct electricity?
Not in solid form
Why can’t a solid ionic compound conduct electricity?
The ions are not free to move
When can ionic compounds conduct electricity?
When they are molten
When they are dissolved
Why can ionic compounds conduct electricity when molten or dissolved?
The ions are now free to move around and act as charge carriers
What is an electrolyte?
A solution that has dissolved ions in it
i.e a solution that can conduct electricity
What is dissociation?
When the lattice of an ionic compound is broken up
Why are solid ionic compounds brittle?
They break easily
Why do solid ionic compounds break easily?
When pressure is put on them
The layers of ions move
Like charged ions line up
The electrostatic repulsion break the crystal
What two kinds of structures can covalent substances form?
Covalent molecular structures
Covalent network structures
What are covalent molecular structures?
Structures made out of covalent molecules
What are intramolecular forces?
The force of attraction existing within a covalent molecule
What is the general magnitude of intramolecular forces?
Strong
What is a polar molecule?
A molecule consisting of atoms, where one atom has a greater electronegativity than the other
The bonding pair is more strongly attracted to that atom
What is a non-polar molecule?
A molecule consisting of atoms, where the atoms have an equal electronegativity
The bonding pair is perfectly shared between them
What does a polar covalent bond cause?
The more electronegative atom will be more negatively charged
The other atom will have a slightly positive charge
What are intermolecular forces?
The forces existing between covalent molecules
These forces hold the crystal lattice of covalent molecular structures together
What is the general magnitude of intermolecular forces?
Weak
Why are covalent molecular structures easy to break apart and have low melting points?
The intermolecular forces are weak and easy to break
What is the general melting point of a covalent molecular structure?
Low
Why does water have a greater density than ice?
The intermolecular forces present in the solid phase result in an open tetrahedral structure, which takes up more space
Why does ice float on water?
Its density is less than that of water
Do covalent molecular structures conduct electricity?
No
What are covalent network structures?
Substances consisting of non-metal atoms covalently bonded to non-metal atoms
What kind of melting points do covalent network structures have?
Extremely high
What is an example of a covalent network structure?
Carbon
What does it mean when a substance has an allotrope?
It has more than one crystalline form
What is an example of an allotrope?
Carbon
It can form both diamond and graphite
Why is diamond such a hard substance?
Each carbon atom is bonded to four other carbon atoms
What is the melting point of diamond?
3500° C
How does graphite differ from diamond? (On a molecular level)
In graphite, the carbon atoms are only bonded to three other carbon atoms
This causes the structure of graphite to occur in layers
Why is graphite so much softer than diamond?
The bonds between the layers of carbon atoms are very weak
They can easily slide over one another
Why can graphite conduct electricity?
The fourth valence electron of graphite is free to move around
What are the properties of covalent network structures?
Extremely high melting points
Solid at room temperature
Hard (except graphite)
Do not conduct electricity (except graphite)
What is the lattice of a metal like?
Regularly spaced positive ions held together by the force of attraction between these positive ions and the ‘sea’ of negative electrons
What are the properties of metallic substances?
Conductors of both heat and electricity
Malleable and ductile
High density
Have lustre
Why are metallic substances malleable and ductile?
The force of attraction existing in its lattice still exists under these conditions
Why do metallic substances have a high density?
The atoms are packed closely together
Why do metals have lustre?
The loosely bound electrons reflect all frequencies of light
This causes a photoelectric effect (shine of a metal)
What is an example of an ionic compound?
Sodium chloride
NaCl
What are three examples of a covalent molecular structure?
Dry ice (CO2(s))
Iodine (s)
Ice (H2O(s))
What are the main differences between a covalent network and a covalent molecular structure?
Covalent network: atoms covalently bonded
Covalent molecular: molecules with intermolecular forces holding them together
What kind of particles exist in a metallic crystal lattice?
Positive metal ions
What force holds a metallic crystal lattice together?
Metallic bond
What is a metallic bond?
The force existing between the ions and the delocalised electrons
Give two examples of a metallic crystal lattice?
Sodium (Na)
Silver (Ag)
