chemistry review. atoms smallest unit of matter. –atoms make up everything (that has mass and...
TRANSCRIPT
Protons (+)
• Determines the identity of the Element
• Represents the Atomic #• Positively charged• Nucleus• Part of the atoms mass
Electrons (-)
• Negatively charged• smallest particles• Outside nucleus• Found in the electron
cloud • Located in energy levels
Electric Charge of the Atom
• Overall charge of an atom is Neutral
• The # of (+) protons = the # of (–) electrons– They cancel each other out
– Remember:• Protons are positive
• Electrons are negative
• Neutrons are neutral (No charge) – They do not count
Nucleus
• Center of the atom
• Made up of Protons and Neutrons
• Makes up the atoms MASS
• Positively Charged!
Energy Levels
• Levels within the electron cloud that hold a specific # of electrons.
– 1st level - 2 electrons– 2nd level - up to 8 electrons
Valence Electrons
• Electrons on the outermost energy level of the atom.
• Determine the atoms chemical properties, including reactivity.
Chemical Symbol
• 1 or 2 letter abbreviation for an element name– 1st letter Capitalized– 2nd letter – always lowercase
• Helium - He
Determining the # of subatomic particles in atoms
Use the following
A = P = E M – A = N
Atomic # = Protons = Electrons
Mass – Atomic # = Neutrons
Arrangement of the Periodic Table
Elements are arranged by:1. By increasing Atomic # and mass
• According to the # of protons the atom has.• Increases from left to right in each period (row)
2. By metals, non-metals and metalloids • According to their physical properties
3. By groups • According to their valence electrons and chemical
properties– Reactivity – How they react chemically in chemical
reactions.
Metals
• Make up most of the elements
• All solid except Mercury
• Has luster (shiny)
• Good conductors of heat and electricity
• Malleable – hammered or shaped into thin sheets
• Ductile – stretched into wires
Nonmetals
• Usually gases or brittle solids
• Poor conductors of heat and electricity– They are insulators
• Right side of the periodic table
• Only 17 nonmetals
Metalloids
• Called Semi-metals
• Share properties of both metals and nonmetals
• Located on the zig-zag line between the metals and nonmetals.
Groups/Families
• 18 Vertical Columns on the periodic table
• Elements have the same # of valence electrons
• Elements share similar chemical properties including reactivity
Periods
• 7 horizontal rows on the periodic table
• Increase by atomic # and mass
• Consist of elements with the same number of energy levels.
Chemical Compounds
• A compound is when 2 or more elements chemically combine.
• The properties of a compound are often very different from the elements themselves.
– Example: Water – H2O• Compound with 2 hydrogen atoms and 1 oxygen atom
Chemical Formulas
• Formulas that use chemical symbols and numbers to represent what makes up a substance.
– NaCl – Sodium chloride (salt)– Na – Sodium, Cl - Chlorine
– H2O – Dihydrogen monoxide (water)– H – Hydrogen, O - Oxygen
– CO2 – Carbon dioxide– C – Carbon, O - Oxygen
Subscripts
• Numbers written below and to the right of a chemical symbol in a formula.
H2O – 2 Hydrogen, 1 Oxygen
• Tells how many atoms of an element are in each molecule.
• Only used if more than one atom is present.
H2SO4
How many atoms of each element are in this compound?
• H = Hydrogen – 2 atoms
• S = Sulfur – 1 atom
• O = Oxygen – 4 atoms
How many elements are there? How many total atoms?• 3 elements 7 atoms
Coefficients
• # placed in front of a chemical symbol or formula
• Identifies the # of molecules of a substance
– 2H2O = 2 molecules of H2O
– 3FeO3 = 3 molecules of FeO3
Coefficients X Subscripts
• To determine the number of atoms using coefficients you multiply the coefficient with the subscript.
• 2H2O - 2 molecules of H2O
= 4 Hydrogen atoms and 2 Oxygen atoms
Using Parentheses
• Multiply the subscript with each element in parentheses.
• Al2(SO4)3
• Al = 2 atoms of Aluminum
• S = 3 X 1 = 3 atoms of Sulfur
• O = 4 X 3 = 12 atoms of Oxygen
Chemical Reactions
• Occurs when one or more substances change to produce one or more different substances.
• Atoms are rearranged to form a totally new substance with properties that are completely different
• Indicators of a chemical reaction– Gas formation – Solid formation – precipitate– Energy change – light, heat, or sound– Color change
Chemical Equations
• Uses chemical symbols and formulas to represent a chemical reaction.
• 2H2 + O2 → 2H2OReactants Yield Products
Sign
Chemical Equations
• Reactants – starting materials in a
chemical reaction.
• Products – substances formed in
a chemical reaction.
Law of Conservation of Mass
• The mass of atoms and molecules is neither created nor destroyed in chemical reactions.– The # of atoms for each element in the reactants
must equal the # of atoms for each element in the products in a chemical reaction.
– Chemical Equations must be balanced.
Chemical Equations Must Be Balanced!
• Law of Conservation of Mass
• The # of atoms in the reactants must equal the # of atoms in the products for each element