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Any substance in the universe that has mass and occupies space is comprised of
Matter
All matter is made up of
atoms
All atoms have the same structure
At the core is a dense nucleus comprised of two
subatomic particles.
• Protons (positively charged).
• Neutrons (no associated charge)
Orbiting the nucleus is another cloud of subatomic
particles = Electrons (negatively charged).
All atoms have a nucleus containing protons and
neutrons, except for one. What is the exception?
hydrogen atom
An atom can be characterized by
the number of protons it has or by its overall mass.
Atomic number
The number of protons in the nucleus.
• Atoms with the same atomic number exhibit the same chemical properties and are considered to belong to the same element
Mass Number
The number of protons plus neutrons in the nucleus.
• Electrons have negligible mass
what determines the chemical behavior of atoms
electrons
Electrons
have energy of position, called potential
energy, occupy energy levels, or electron shells, of an atom, which are actually complex, three-dimensional volumes of space called orbitals.
Orbitals are where electrons are most likely to be found
probability clouds
Electron shells can have up to how many orbitals?
4, which can each hold up to 2 electrons
Atoms that have which type of electron orbitals tend to be more reactive?
incomplete
When do electrons release energy
As electrons move to a lower energy level, closer to the nucleus, energy is released
Ions
atoms that have gained or lost one or more electrons
Cations vs Anions
c= positive a= negative
Isotopes
atoms that have the same number of protons but
different numbers of neutrons.
• Most elements in nature exist as mixtures of different isotopes
radioactive decay
Some isotopes are unstable and break up into particles with lower atomic numbers
molecule
a group of atoms held together by energy in
the form of a chemical bond
3 principal types of chemical bonds
Ionic, Covalent, Hydrogen
Ionic Bonds
involve the attraction of opposite
electrical charges.
• Molecules comprised of these bonds are often
most stable as crystals
covalent bonds
a chemical bond that involves the sharing of electrons to form electron pairs between atoms
Polar Molecule
a molecule with an uneven distribution of electrons, resulting in a separation of charge
Polar covalent bonds
form when the shared electrons of
a covalent bond spend more time in the vicinity of a
particular atom.
Hydrogen Bonds
are weak electrical attractions between the
positive end of one polar molecule and the negative end of another.
• Each atom with a partial charge acts like a magnet to bond weakly to another polar atom with an opposite charge
Unique Properties of Water
Water Stores Heat:
• Water temperature changes slowly and holds temperature well.
Water Forms Ice:
• Few hydrogen bonds break at low temperatures.
• Water becomes less dense as it freezes because hydrogen bonds hold water molecules farther apart.
Water Evaporates:
• Water requires tremendous energy to vaporize because hydrogen bonds must be broken.
• When water vaporizes, it takes this heat energy with it, allowing for evaporative cooling
If you leave a glass of water with ice on a table, will the level of water change as the ice
melts?
No, the water level in a glass will not change when ice melts in it because the volume of water displaced by the floating ice is equal to the volume of water that will be produced when the ice melts; essentially, the ice takes up the same amount of space as the water it becomes when melted.
hydrophilic
molecules are attracted to water and dissolve easily in it.
• These molecules are also polar and can form hydrogen bonds
hydrophobic
molecules are repelled by water and do not dissolve.
• These molecules are nonpolar and do not form hydrogen bonds.
“like dissolves like”
What happens when the covalent bond within a water molecule sometimes breaks spontaneously
This produces a positively charged hydrogen ion H^+ and a negatively charged hydroxide ion H^-
A positively charged hydrogen ion is equivalent to
what subatomic particle?
A positively charged hydrogen ion is equivalent to a proton
Explanation: When a hydrogen atom loses its single electron, it becomes a positively charged hydrogen ion, which is essentially just a proton left behind
how can the amount of ionized hydrogen from water in a solution can be measured?
as pH
The pH scale is logarithmic
which means that a pH scale difference of 1 unit actually represents a 10-fold change
in hydrogen ion concentration.
pH of pure water
7
Acid
any substance that dissociates in water and increases the H+
• Acidic solutions have pH values below 7
Base
any substance that combines withH+
when dissolved in water. Basic solutions have pH values above 7.
what is the pH in most living cells and their environments
fairly close to 7
Organisms use buffers to minimize pH disturbances
a chemical substance that takes up or releases
hydrogen ions
