Unit 2: Chemistry Honors Test Study Guide
Just think about magnets
Periodic Table
Mendeleev’s periodic table: groups elements by their properties
Modern periodic tables: group elements by their atomic number and properties
Properties of d-block/f-block: do not vary much
Properties of s-block/p-block: do vary
Periods (rows) of the periodic table: determined by electron configuration.
Groups (columns) of the periodic table: determined by the number of valence electrons (causes them to react
similarly)
Atoms
Atoms: the building blocks of all matter
Atoms contain: positive (protons), neutral (neutrons), and negative (electrons) particles.
Nuclei: Protons/neutrons are found in the nucleus and have a positive charge overall.
Dense Nucleus: all atoms have a dense nucleus that makes up most of its mass.
Atoms of the same element: Must have the same number of protons but neutrons can change
Atomic Mass
Atomic mass is a relative measure meaning:
• Everything is measured based off of carbon 12
Atomic mass is a weighted measure meaning
• The atomic mass is a weighted average of all the isotopes and how common they are.
A relative mass scale makes counting atoms possible:
The atomic mass tells you how many grams one mole of an element weighs.
carbon 12 amu 1 mole of carbon 12grams
02 1023
Atomic Radii
The atomic radius: the distance from the nucleus to the outermost electron shell
Atomic radii are related to electron configurations by:
1. Number of electron shells/energy levels (and shielding)
2. Effective nuclear charge
When atoms become ions their radii change:
Cations(+): become smaller because they have more protons than electrons which means the pull of the nucleus
, becomes stronger, and therefore the atomic radius decreases.
Anions(-): become larger because they more electrons than protons which means the pull of the nucleus decreases,
and therefore the atomic radius increases.
The radii of atoms is expressed in picometers
1 pm 10 meters
middle smallest
iiteitai.it 1 samesheildingenergylevels 1 Samesheildingenergylevels
onsa.nessereeegygiiEe'moms
Electrons
Electrons: negative charged particles in an atom
Valence electrons: the electrons found on the outermost shell in the (s/p blocks)
Electrons only exist in specific energy states/levels for atoms of each element
Ground vs. excited states: when electrons absorb energy, they move to a higher level (excited), whereas when
electrons lose energy, they move to a lower level (ground).
Electrons have wavelike properties
• Instead of moving in straight lines, they move in waves of energy around the nucleus
• They can spread out instead of being in an exact location
they can only have certain energy levels (like a guitar can only play certain notes)
Orbitals: a region of space around an atom’s nucleus where an electron is most likely to be found
Electrons fill in the lowest- energy orbitals first
No electrons can fill in higher levels before the lower one is filled first.
Removing electrons from atoms to form ions: Ionization
Ionization requires different amounts of energy for each element
Compound: a substance made when two or more different elements chemically bond
Only outer electrons (valence electrons) are involved in compounds.
Electronegativity
Electronegativity: measures how strongly an atom pulls shared electrons in a chemical bond.
atoms have different abilities to capture electrons using electronegativity
Nobel gasses cant have electronegativity because their outer shells (valence electrons) are already full.
Just think about magnets
Periodic Table
Mendeleev’s periodic table: groups elements by their properties
Modern periodic tables: group elements by their atomic number and properties
Properties of d-block/f-block: do not vary much
Properties of s-block/p-block: do vary
Periods (rows) of the periodic table: determined by electron configuration.
Groups (columns) of the periodic table: determined by the number of valence electrons (causes them to react
similarly)
Atoms
Atoms: the building blocks of all matter
Atoms contain: positive (protons), neutral (neutrons), and negative (electrons) particles.
Nuclei: Protons/neutrons are found in the nucleus and have a positive charge overall.
Dense Nucleus: all atoms have a dense nucleus that makes up most of its mass.
Atoms of the same element: Must have the same number of protons but neutrons can change
Atomic Mass
Atomic mass is a relative measure meaning:
• Everything is measured based off of carbon 12
Atomic mass is a weighted measure meaning
• The atomic mass is a weighted average of all the isotopes and how common they are.
A relative mass scale makes counting atoms possible:
The atomic mass tells you how many grams one mole of an element weighs.
carbon 12 amu 1 mole of carbon 12grams
02 1023
Atomic Radii
The atomic radius: the distance from the nucleus to the outermost electron shell
Atomic radii are related to electron configurations by:
1. Number of electron shells/energy levels (and shielding)
2. Effective nuclear charge
When atoms become ions their radii change:
Cations(+): become smaller because they have more protons than electrons which means the pull of the nucleus
, becomes stronger, and therefore the atomic radius decreases.
Anions(-): become larger because they more electrons than protons which means the pull of the nucleus decreases,
and therefore the atomic radius increases.
The radii of atoms is expressed in picometers
1 pm 10 meters
middle smallest
iiteitai.it 1 samesheildingenergylevels 1 Samesheildingenergylevels
onsa.nessereeegygiiEe'moms
Electrons
Electrons: negative charged particles in an atom
Valence electrons: the electrons found on the outermost shell in the (s/p blocks)
Electrons only exist in specific energy states/levels for atoms of each element
Ground vs. excited states: when electrons absorb energy, they move to a higher level (excited), whereas when
electrons lose energy, they move to a lower level (ground).
Electrons have wavelike properties
• Instead of moving in straight lines, they move in waves of energy around the nucleus
• They can spread out instead of being in an exact location
they can only have certain energy levels (like a guitar can only play certain notes)
Orbitals: a region of space around an atom’s nucleus where an electron is most likely to be found
Electrons fill in the lowest- energy orbitals first
No electrons can fill in higher levels before the lower one is filled first.
Removing electrons from atoms to form ions: Ionization
Ionization requires different amounts of energy for each element
Compound: a substance made when two or more different elements chemically bond
Only outer electrons (valence electrons) are involved in compounds.
Electronegativity
Electronegativity: measures how strongly an atom pulls shared electrons in a chemical bond.
atoms have different abilities to capture electrons using electronegativity
Nobel gasses cant have electronegativity because their outer shells (valence electrons) are already full.
