Chemistry Lecture 1 Flashcards
Atom
the smallest part of a substance that cannot be broken down chemically, makes up an element
Element
composed of only one type of atom
Subatomic particles
Electrons, protons, and neutrons.
Nucleus
At the center of an atom, contains one or more protons and may also contain neutrons.
Electron cloud
Created by the whirl of electrons around the nucleus.
Atomic number
The total number of protons in an atom.
Mass number
The total number of protons and neutrons in an atom.
Isotopes
Atoms with the same number of protons but different numbers of neutrons.
Atomic mass
The actual mass of an atom of a specific isotope, measured in atomic mass units (amu) or daltons.
Atomic weight
The average mass of an element, including different isotopes in proportion.
Elements
- Purest substances
- Cannot be broken down further chemically
- Present in living and non-living matter
- Total of 118 elements, 94 natural, 24 derived
Atoms
- Protons balance electrons
- Electrically neutral
Electron Cloud
- Series of concentric shells
- First shell (closest to nucleus) is lowest energy level
Valence Shell
- Outermost shell
- Unfilled = reactive
- Electrons are donated, received, or shared
Full outer shells are inert
- Stable
- Examples: helium, neon
- Noble gases
Octet Rule
- Atoms aim for 8 electrons in valence shell
- Achieve stability
Ions
- Gained or lost electrons
- Net positive (cation) or negative (anion) charge
- Examples: +1, +2, +3, -1, -2, -3, -4
Molecules
- Formed by atoms sharing electrons
- Example: O2 (oxygen)
Compounds
- Combination of different elements
- Examples: NaCl (table salt), H2O (water)
Ionic Bonds
- Strong when not in solution, weak in solution
- Formed by transfer of electrons
Covalent Bonds
- Strong bonds formed by sharing electrons
- Examples: single, double, triple bonds
Electronegativity
- Influenced by atomic radius and nuclear charge
- Oxygen has high electronegativity
Hydrogen Bonds
- Weakest bond, between polar molecules
- Properties: surface tension, heat capacity, solvent properties
