Unit 1: Structure and Properties of Matter Flashcards
Atomic Radius
Increases as you go down a group because you are adding extra energy levels.
Decreases as you go across a period from left to right because you are adding more protons and electrons so there is a greater force of attraction, therefore, pulling the electron cloud into the nucleus more tightly.
Ionic Radius (Cations)
Cations are smaller than the neutral atom because they have lost an energy level.
Ionic Radius (Anions)
Anions are larger than the neutral atom because there are one or more electrons and the nucleus cannot pull the electrons in as tightly. The extra electrons causes more repulsion in the outer energy level, increasing the size of the electron cloud.
First Ionization Energy
First ionization energy is the energy required to remove the first electron from a neutral gaseous atom.
Decreases as you go down a group because the valence electrons are further from the nucleus (shielding from the inner energy levels) for the larger atoms and can be removed more easily (with less energy).
Increases as you go across a period because the atoms are getting smaller and the outer electrons are closer to the nucleus and require more energy to be removed.
An atom has a HIGHER IONIZATION ENERGY if the valence electrons are harder to remove.
If the valence electrons are easier to remove, an atom has a LOWER IONIZATION ENERGY.
If an atom has a SMALLER atomic radius, it has a HIGHER ionization energy because it has more protons and electrons, therefore, it is harder to remove the valence electrons from the outer energy level.
The less energy levels an atom has, the higher the ionization energy because the closer the valence electrons are to the nucleus, the harder they are to remove.
Electron Affinity
X(g) + electron —> X⁻ + energy
Electron affinity is the energy released when an atom gains an electron.
Decreases as you go down a group because the atoms are getting larger and it is more difficult for the nucleus to attract an extra electron (it is further, so force is weaker, releasing less energy).
Increases as you go across a period because the atomic radius is decreasing, so the electrons are more strongly attracted to the nucleus (it is closer, so force is stronger, releasing more energy).
Fluorine has the highest electron affinity.
Electronegativity
A number that describes the relative ability of an atom to attract electrons to itself when bonded – electrons are pulled towards the atom with a higher electronegativity.
Polar Covalent Bond
Found when two atoms with different electronegativities share electrons.
***Unequal sharing.
Ex. (H — O) —> Oxygen is the electron hog (pulling electrons from hydrogen to itself since it has the higher electron affinity.
Polar Molecule
A molecule where there is an uneven distribution of electrons, so that there is a partial positive charge at one end of the molecule and a partial negative charge at the other end of the molecule. Ex. CO (carbon monoxide).
Nonpolar Molecule
A molecule where the electrons are evenly distributed, so that there are no locallized charges. Ex. CO₂ (carbon dioxide) —> molecule is nonpolar due to linear shape (bond dipoles cancel).
Intramolecular Forces
Force holding atoms together in (within) a compound … IONIC OR COVALENT BONDS (chemical bonds)
Intermolecular Forces
The attractive forces between molecules. Also called Van der Waals forces: the weak forces of attraction between molecules, including dipole-dipole forces, hyrdogen bonding and London dispersion forces.
Intermolecular Forces and Physical Properties:
- physical state (s), (l), (g)
- melting point
- boiling point
- surface tension —> a force which causes the surface layer of a liquid to behave like a stretched elastic membrane. Molecules hold and stick together, creating a network of layers that acts as a thin, elastic sheet or skin.
Ex. When insects run across water due to the water having a high surface tension.
Intermolecular Forces: London Dispersion Forces
A weak attractive force between all molecules (atoms), including non-polar molecules and unbonded atoms, caused by the temporary imbalance of electrons.
London forces are the weakest intermolecular force. London forces get stronger as the number of electrons increases, so the boiling point also increases.
Summary: The more electrons, the larger the molecule, and the higher the boiling point.
Intermolecular Forces: Dipole-Dipole Forces
An intermolecular force of attraction that forms between the slightly positive end of one POLAR molecule and the slightly negative end of an adjacent POLAR molecule.
***Molecules must be polar.
Dipole-dipole forces are stronger than London forces.
The stronger the intermolecular force, the higher the boiling point.
Intermolecular Forces: Hydrogen Bonding
An unusually strong dipole-dipole force between a hydrogen atom attatched to a highly electronegative atom (N, O, or F) and a highly electronegative atom in another molecule.
***Look for H-F, H-O, or H-N.
Drops On A Penny Explanation
Materials:
- Oil and water
- 2 pennies
- 2 droppers
- Paper towel
Water (H₂O): With water, there is a strong surface tension due to the hydrogen bonds between molecules. Because of the strong force of attraction (hydrogen bonding), a penny is able to hold more drops of water. It is also important to note that water is a polar molecule and has polar bonds, meaning the hydrogen bonds (stongest intermolecular force) are holding the molecules together more tightly.
Oil (C₈H₁₈): Oil is made of hydrogen and carbon atoms and is a nonpolar molecule (linear structure, so bond dipoles cancel), meaning, it cannot form hydrogen bonds. Oil has London forces holding the molecule together, so the force of attraction is weaker, and therefore, a penny can’t hold as many drops of oil as it can with water.
