Inter and Intra Molecular Forces

• atom: the smallest particle of a chemical element that can exist.
• A covalent bond is a bond between two non-metal atoms in which the electrons are shared between the atoms.
• In a polar covalent bond, the electrons are not equally shared because one atom spends more time with the electrons than the other atom.
• An ionic bond is a bond that forms due to the complete transfer of valence electron(s) between atoms
• An ion is a charged atom or molecule, it is charged because the number of electrons do not equal the number of protons in the atom or molecule.
• a chemical reaction is breaking and forming bonds
• electronegativity is a measure of the tendency of an atom to attract elements.
• Atoms always want a full valence electron shell. They achieve this goal through bonding chemically (meaning they gain/lose or share electrons with other atoms or molecules). When atoms do this, they are making or breaking chemical bonds.
• A cation is a positively charged ion, and an anion is a negatively charged ion.
• The periodic table organizes the elements left to right according to atomic number, which is also the number of protons (positive). The number of electrons is equal to the number of protons, or the atomic number.
• A chemical reaction creates a brand new substance, while physical changes don’t create new substances.
• Atoms are always neutral.
• On a periodic table, the group number is determined by the number of valence electrons while the period number is determined by the number of electron shells.
• Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Each atom has a set of electro negativity value (0-4). A higher value will attract bonding electrons more, while a lower value will attract bonding electrons less.
• if the difference between the 2 atom is within the range 0-0.4 it is a non polar covalent bond
• if the difference between the 2 atoms is within the range 0.4-1.8 it is a polar covalent bond
• if the difference between the 2 atoms is within the range 1.8-4 it is a ionic bond
• the further apart bonded elements are on the periodic table, the more likely it is a ionic bond.
• netrons equal the mass of an element subtracted by the atomic number
• in vsepr models, a dashed wedge means it is going into the plane of the paper, a solid wedge means it is coming out of the paper
• intermolecular forces are the forces that determine the physical properties of a substance. They are also the forces between the molecules, and they determine how close the particles are.
• Intramolecular forces are the forces within the molecule itself (bonding). It include chemical bonds and creates new substances.
• In a bond, the element with a higher electronegativity has a partial negative charge (delta minus) because the electrons spend more time closer to that atom. The element with a lower electronegativity has a partial positive charge (delta plus) because the electrons spend less time with the atom.
• Dipole-Dipole Forces: Unequal sharing of electrons results in dipoles - a molecule with a negative and positive end. The dipoles developed attractive forces between the positive end of one polar molecule and the negative end of another polar molecule.
• Dipole-Dipole forces are commonly seen in interactions among polar molecules - molecules that have polar covalent bonds.
• Hydrogen Bond Forces are a special dipole-dipole force in molecules containing N-H, O-H, or F-H bonds. The large difference in electronegativity between the H atom and the N, O, or F atom leads to a highly polar covalent bond (ie. a bond dipole)
• Hydrogen bond forces are commonly seen in molecules containing Nitrogen and Hydrogen (N-H), Oxygen and Hydrogen (O-H), and Flourine and Hydrogen (F-H) bonds, it is also very common in water.
• Polar Covalent, Non-Polar Covalent, and Ionic Bonds are all intramolecular forces.
• Dipole-dipole, Hydrogen Bond, and London Dispersion Forces are all intermolecular forces.
• A London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.
• London dispersion forces are commonly present between any two molecules (even polar molecules) when they are almost touching. These forces are stronger between larger molecules.
• Strongest to Weakest Intermolecular Forces:

  1. Hydrogen Bond Forces
  2. Dipole-dipole forces
  3. London dispersion forces
• 2 bonds around a central atom will have a linear shape
• 3 bonds around a central atom will have a tetrahedral shape
• 2 bonds and one lone pair around a central atom will have a bent shape
• 4 bonds around a central atom will have a tetrahedral shape
• 3 bonds and 1 lone pair around a central atom will have a trigonal pyramidal shape
• 2 bonds and 2 lone pairs around a central atom will have a bent shape
• 5 bonds around a central atom will have a trigonal bypryamidal shape
• 6 bonds around a central atom will have an octahedral shape