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Plovdiv entrance exam chemistry with complete solutions 2024_2025
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Plovdiv entrance exam chemistry with complete solutions 2024_2025
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Plovdiv entrance exam chemistry withcomplete solutions 2024/2025
what is a chemical element
atoms with the same number of protons in their atomic nuclei
what is an isotope
variants of the same chemical element with different number of neutrons, they
share the same proton number
what is an isobar
atoms or ions that have the same mass number but different atomic number
atomic mass
The average mass of all the isotopes of an element
Principal energy levels (shells)
main energy levels in which the electrons orbit the nucleus
what is an orbital
electrons are likely to be found
different shapes of the orbitals
s: spherical
p: dumbbell shaped
atomic radius trend
decreases from left to right as nuclear charge is increasing
Increases down a group as electrons occupy higher energy levels increasing the
distance from the nucleus
what is ionisation energy
, the minimum amount of energy required to remove 1 mole of electrons from one
mole of atoms in a gaseous state
ionisation energy
across a period increases due to increasing nuclear charge
Down a group decreases as electrons due to weaker nuclear attraction
what is electron affinity
the energy taken in or given off when an electron is added to an atom
electron affinity
increases left to right due to atoms ability to attract electrons
Decreases down the group due to higher nuclear distance
what is electronegativity
a measure of the tendency of an atom to attract a bonding pair of electrons
electronegativity trend
increases left to right
Decreases down the group
ionic radius cations(postive ions) and anions(negative ions)
positive: smaller than parent ions as electron removed
Anions:
Larger due to more electrons
melting and boiling point
increase across group due to stronger intermolecular forces
Decrease down a group due to weaker intermolecular forces
properties of metals and non metals
metals: shiny, conductive, malleable and ductile
Non metals: dull non conductive and brittle
element oxidation state
0
what determines polarity
electronegativity
what is automatically non polar
hydrocarbons
Symmetrical: all molecules round the same
what is automatically polar
hydrogen bonded to nitrogen oxygen or fluorine
What is a coordinate covalent bond?
a covalent bond in which one atom contributes both bonding electrons
sigma bond
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