Unit 1 - Chemical Changes and Structure Flashcards
(34 cards)
What is periodicity?
the occurence of patterns in the periodic table
What happens as you go down a group in the periodic table?
there is an extra occupied energy level of electrons
What happens as you go across the period in the periodic table?
the atomic number increases by one for each element, but the number of energy levels stays the same.
What is the atomic size?
the covalent radius is half the distance between the nuclei of two bonded atoms of the element.
Why is there no data for noble gases?
they have full energy levels and do not need to bond (monatomic)
Describe the observed trend in atomic size across a period (decreases)
Across a period the covalent radius decreases.
Atoms within a period have the same number of occupied energy levels, but have an increase of one proton from one element to the next.
Increased positive charge on the nucleus increases the attraction for the electrons in the outer energy level and are pulled closer to the nucleus, making them smaller.
Describe the observed trend in atomic size down a group (increases)
Elements within the same group have one more occupied energy level with each succeeding element, therefore the size of the element is larger.
What is the first ionisation energy?
The first ionisation energy is the energy required to remove one electron from each atom of one mole of gaseous atoms.
What is the second ionisation energy?
The second ionisation energy is the energy required to remove one electron from each singly positive ion of one mole of the gaseous ions.
What is electronegativity?
a measure of the attraction an atom involved in a bond has for the electrons of the bond.
What happens when electronegativity is high?
The higher the electronegativity, the more strongly the atom/nucleus attracts electrons towards it.
Explain the trend in electronegativity across a period.
Across a period, the electronegativity increases as the nucleur charge increases. This makes the nucleus have a stronger electrostatic attraction for electrons.
Explain the trend in electronegativity down a group.
Down a group, electronegativity decreases as atomic size increases due to the increase in the number of occupied energy levels and the electrons are further from the nucleus. The nucleus is also more screened by inner occupied energy levels.
Describe the metallic bond
The electrostatic force of attraction between the positively charged ions and the delocalised electrons.
The metallic structure is a giant lattice of positively charged ions in a sea of delocalised electrons.
properties:
-electrical conductors
-high melting points
-good thermal conductors
across a period:
- the electrical conductivity increases as there are more delocalised electrons.
- melting points of metals increases as the positive core is increasing in charge.
down a group:
- melting points of metals decrease, there are more occupied energy levels and so the nucleus is further away from the delocalised electrons.
Describe the covalent bond
A single covalent bond consists of one shared pair of electrons.
Can have pure/non-polar or polar covalent bonds.
properties of covalent network substances:
-very high melting points
-very hard substances
- do not conduct electricity
-insoluble in water.
Describe the pure/non-polar covalent bond
When atoms of the same element form a covalent bond, the electrons are shared equally. This is because the atoms have the same electronegativity.
Describe the polar covalent bond
When atoms of different elements share electrons. Atoms with different electronegativity values will share the pair of bonding electrons unequally forming partial changes of a permanent dipole.
How are bonding electrons shared between atoms?
The atom with the highest electronegativity will attract the bonding electrons closer towards it, becoming slightly negative. The other atom is left slightly electron, becoming slightly positive.
Describe the ionic bond
Due to periodic trends in electronegativity, elements far apart in the periodic table are more likely to form ionic rather than covalent bonds.
An ionic bond is the electrostatic attraction between the positive and negative ions, these are oppositely charged ions together in a 3D crystal lattice.
properties:
-high melting point.
-do not conduct electricity when solid as ions are not free to move.
-conduct electricity when molten or in solution as ions are free to move.
-soluble in water.
What are Van Der Waals forces of attraction?
The forces of attraction that hold discrete atoms (noble gases) and discrete molecules (diatomics) together in the liquid and solid state are called Van Der Waals forces of attraction. All van der waals forces are weak.
What are the types of Van Der Waals forces?
London Dispersion Forces
Permanent-Dipole Permanent-Dipole (including Hydrogen Bonding)
London dispersion forces
Very weak, resulting in atoms having very low melting and boiling points.
How are London Dispersion Forces caused?
An uneven distribution of the constantly moving electrons around the nucleus. LDFs are formed as a result of electrostatic attractions between temporary (instantaneous) dipoles and induced dipoles caused by the movement of electrons.
What is a temporary or instantaneous dipole?
One side of the atom has a slightly negative charge and the other side a slightly positive charge.
