Notes On Chemistry

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Chemistry H Ch.7-8 Test Study Guide
Ion formation, gain/lose electrons:
- Ions are formed when an atom gains or loses electrons and get charged.
- If an atom gains electrons, an atom gets negatively charged (Anion).
- Similarly if an atom looses electrons, the atom becomes positively charged
Ionic Compounds, properties:
- A compound that is composed entirely of ions is called an ionic compound. - Ionic compounds are formed from a metal and a non-metal.
- Ionic compounds are hard and brittle.
- Ionic compounds conduct electricity when they are dissolved in water.
- Ionic solids are good insulators.
Anions/ Cations:
- Positively charged ion = Cation (left side of periodic table)
- Negatively charged ion = Anion (Right side of periodic table)
Octet Rule: - Octet Rule: The octet rule states that atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons.
Draw Lewis Dot structures:
For Compounds
- 1. Find the total number of valence electrons.
- 2. Find the number of electrons needed to make the atoms have a full set. - 3.Determine the number of bonds in the molecule.
- 4.Choose a central atom.
- 5.Draw a skeletal structure.
- 6. Place electrons around outside atoms.
- 7. Place remaining electrons around the central atom.
Lewis structure chart for single elements
Writing formulas for binary ionic compounds:
- Example Barium Sulfide Monatomic ions:
- Ions that are formed using 1 atom
- Monoatomic = “one atom”
- Example: Ca2+
Polyatomic ions:
- Ions that are formed from a group of ions
- Polyatomic = “many atoms”
- Example: CO32- Covalent bonds:
- Bond that is formed by a shared pair of electrons between two atoms.
- Nonpolar covalent bond: A covalent bond where the electrons are shared equally between the two atoms. - Polar covalent bond: A covalent bond where the electrons are shared unequally; one atom is more electronegative than the other. Ionic Bonds: Causes the two atoms to become neutral or zero charge
- For example, ions with one extra electron would make an ionic bond with an ion with one less electron causing. The ion with one less electron would rip off the electron from the positively charged one.
Type of Bond Difference of electro negativities
Nonpolar covalent Less than 0.4
Polar covalent Between 0.4 and 2.0
Ionic Greater than 2.0 Single, double, triple covalent bonds:
Type of Covalent Bond Characteristics
Single - 1 shared pair of electrons
Double - 2 shared pairs of electrons
Triple - 3 shared pairs of electrons Diatomic molecules:
- Molecules made from two of the same atoms (Have no bond angle). o Ex: Dioxide (O2, N2)
Carbon dioxide:
- A colorless, odorless gas produced by burning carbon and organic compounds and by respiration. It is naturally present in air (about 0.03 percent) and is absorbed by plants in photosynthesis.
- Formula: CO2
- Molecular Geometry: Linear
- Nonpolar
- A colorless, transparent, odorless, tasteless liquid that forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms.
- Formula: H2O - Molecular Geometry: Bent
- Polar
- The chemical element of atomic number 7, a colorless, odorless unreactive gas that forms about 78 percent of the earth's atmosphere.
Crisscross method (ionic compounds): Electron configurations of ions: Ammonia:
- A colorless gas with a characteristic pungent smell. It dissolves in water to give a strongly alkaline solution.
- Formula: NH3, Formula of ion (Ammonium): NH4+
- Exception to ionic bonding rule
Hybrid orbitals:
- When an atom approaches another atom to form a bond, the orbitals of its electrons may be perturbed, or changed. This combination is called
“hybrid orbitals”
Bond length:
- Going down a group: forms longer bonds. o Atoms grow larger and weaker as you go down