chemistry

• atomic number is the number of protons in the nucleus of an atom, which is equal to the number of electrons in the outermost shell
• mass number is the total number of protons and neutrons in the nucleus of an atom
• the periodic table arranges elements by increasing atomic number
• isotopes are atoms with different numbers of neutrons but same atomic number
• groups on the periodic table have similar chemical properties because they have the same number of valence electrons
• groups are columns on the periodic table that contain elements with similar properties
• periods are rows on the periodic table that contain elements with similar electron configurations
• relative atomic mass (A) is the weighted average of all naturally occurring isotopes of an element
• elements in group 1 have one valence electron
• a molecule is two or more atoms bonded together
• an ion is an electrically charged particle formed when one or more electrons have been gained or lost
• elements are arranged according to atomic number
• periodic table families include:

  • alakali metals
  • non alakali metals
  • halogens
  • noble gases
  • boron family
  • carbon family
  • nitrogen family
• atomic orbitals are the regions of space around the nucleus where electrons can be found
• the s orbital has spherical shape, while p orbitals have dumbbell shapes
• electron configuration refers to how many electrons occupy each energy level
• ionization energy is the amount of energy required to remove an electron from an atom or ion
• metalloids are elements that exhibit properties between metals and non-metals
• atomic radius is the distance between the nucleus and the outermost electron shell in an atom
• more protons=smaller atomic radius
• shielding effect: the reduction in the net positive charge felt by the valence electrons due to the repulsive effect the core electrons have on valence electrons (reduces columbic attraction)
• coulombic attraction: the attractive force between protons & electrons
• coulombic attraction decreases down a group (increases left to right across a period)
• ionic radius is the distance between the positive and negative ions in an ionic compound
• groups 1a-3a loose valence electrons & become cations (positively charged ions)
• groups 5a-7a gain additional valence electrons to become anions (negatively charged ions)
• octet rule: the number of electrons in the outermost energy level of an atom is equal to the number of protons
• electronegativity: the ability of an atom of an element to attract electrons towards itself in a chemical bond
• noble gases do not have electronegativity values & do not loose/gain electrons
• electronegativty increases up a group and left to right across a period
• Bohr model: electrons are located in an atomic orbital (sublevels of an energy level)

  • closer energy level has electrons that have a stronger attraction to the nucleus
  • to move from level to level, an atom must gain or loose a quantum of energy
  • 7 energy levels & 4 sublevels= s, p, d, f
  • 1= s orbital, 2= s, p orbitals, 3= s, p, d, orbitals, 4-7= s, p, d, f orbitals
  • electrons in the same orbital must have opposite spins
  • electrons occupy empty orbitals first
• C= wavelength times frequency


  C= speed of light (3.00 times 10^8 m/s)
• photoelectric effect: when an atom is given excess energy, it jumps to a higher energy level (excited state)