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Chemistry Review
Chapter 4
- atom: is the smallest particle of an element that retains its identity in a chemical reaction.
Democritus (400 B.C - 370 B.C)
- Atoms are indivisible and indestructible.
- Matter is made up of atoms.
- No explanation for chemical behavior.
- NO experiment support.
Dalton ( 1776 - 1844)
- all elements are comprised of tiny indivisible particles called atoms.
- Atoms of the same element are identical.. atoms of any element are different from those of another.
- Atoms combine in whole number ratios to from compounds.
- Chemical reactions occur when atoms separate, join, or rearrange.
- During a chemical reaction atoms are never created or destroyed.
- (experimental)
J.J Thompson (1856 - 1940)
- Cathode ray.
- Subatomic Particles.
- Model of an atom.
Rutherford (1871 - 1837)
- The gold Foil experiment.
- Empty space.
- Positively charged center (nucleus)
Bohr
- Energy Levels.
- Atomic Number: the number of protons in the nucleus.
- Mass number: the total number of protons and neutrons. (mass number - atomic number)
Isotopes: atoms that have the same number of protons, but differ in the number of neutrons.
- Isotopes of an element have different mass numbers.
- Ex. Neon 20 … 10 protons, 10 neutrons, 10 electrons. Neon 21… 10 protons, 11 neutrons, 10 electrons.
- Atomic Mass: is a weighed average mass of the atoms in a naturally occurring sample of the element. Mass of each isotope x natural abundance. Express as a decimal then add the products.
(12.000 amu x 0.9889) + (13.003 x 0.0111) = 12. 001 amu
- Period: horizontal row on the periodic table. (properties vary as you move across.)
- Group: vertical columns on the periodic table. ( elements with in a group have similar properties)
Chapter 5
-The Bohr Model: proposed that an electron is found only in specific circular paths, or orbital, around the nucleus.
- Energy Levels: the fixed energies an electron can have.
- Quantum: the amount of energy required to move an electron from one energy level to another.
- Quantum Mechanical Model: the modern description of the electrons in an atom. Restricts the energy of electrons to certain values. Determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.
- Atomic Orbitals: the region of space in which there is a high probability of finding an electron. (Represented with a number 1,2,3,4…..)
-electron Configurations…the ways electrons are arranged in various orbitals.
- Aufbau Principle: electrons occupy the lowest energy level first.
-Pauli Exclusion Principle: an atomic orbital may describe at most 2 electrons. They must have opposite spins.
- Hund’s Rule: that electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.
Chapter 7
- Valence Electrons: electrons in the highest occupied energy level of an element’s atom.
- To find the number of valence electrons in an atom of an element, look at it’s group number. (ex. Elements in group 1A hydrogen, lithium, sodium, potassium all have 1 valence electron.
- Electron Dot Structures: display the number of valence electrons in and element. H Mg Ne
- Octet Rule: in forming compounds, atoms tend to achieve the electron configuration of a noble gas. (8)
- Cation: loss of a valence electron. A positively charged ion.
- Anions: the gain of a negatively charged electrons by a neutral atom.
- Halide ions: when atoms of chlorine and other halogens gain electrons.
- Ionic compounds: composed of cations and anions. Usually of metal cations and nonmetal anions. Usually electrically neutral.
- Ionic bonds: the electrostatic forces that hold ions together in ionic compounds.
- Chemical Formula: shows the kinds and numbers of atoms in the smallest representative unit of a substance. (NaCl)
- Formula Unit: the lowest whole number ratio of the ions in an ionic compound. (Na+ Cl- = 1:1 =NaCl)
- Metallic Bonds: consists of the attraction of the free-floating valence electrons for positively charged metal ions. They hold metals together. (sea of electrons)
- Alloys: mixtures composed of two or more elements, at least one of which is a metal. (brass is an alloy of Cu and Zn)
Chapter 9