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Chapter 6: The Structure of Matter
Transcript of Chapter 6: The Structure of Matter
Monoatomic element - the basic unit consists of one atom. Ex: Na or He
Diatomic Element - the basic unit consists of two atoms of the same kind bonded together. Ex: O2 or Cl2
Polyatomic Element - the basic unit consists of three or more atoms of the same kind bonded together. Ex: O3 of S8
Compound - the basic unit consists of two or more different kinds of atoms bonded together. Ex: NaCl or C6H12O6
Mixture - the basic units are not all the same; it could consist of any combination of two or more of the above NOT bonded together. Sec 1: Compounds and Molecules
attractive forces that hold different atoms or ions together in a compound.
transferring e- (losing or gaining)
Chemical Bonds Why Bond? -- Stability Octet Rule
most atoms form bonds in order to have 8 valence e-
full outer energy level
like the Noble Gases!
Stability is the driving force behind bond formation!
Formula and Structure Chemical Formula Shows:
Elements in a compound
Ratio of their atoms
The arrangement of atoms in a substance
H2O 2 Hydrogen 1 Oxygen H H O Chemical Structure Shows how a compound’s atoms or ions are connected (the way they are arranged)
Bond length - distance between the nuclei of 2 bonded atoms
Bond angle - the angle formed by two bonds to the same atom
Different structure = different properties ! Models Represent Structures Ball and Stick Model:
atoms are represented by balls; the bonds that hold the atoms together are represented by sticks
chemical symbols are used to represent the atoms
show the space occupied by atoms Chemical Bonds Bonds can bend, stretch, and rotate without breaking.
Bonds can be represented by flexible springs.
Most reported bond lengths are average distances.
Bonds hold atoms together tightly. Types of Structures The chemical structure of a compound determines the properties of that compound!
Types of Structures:
Compound Networks - strongest bonds, form strong solids, very high melting and boiling points
Ion Networks - positive and negative ions attracted, high m.p. and b.p.
Molecule Networks - held together by weak bonds Hydrogen Bonds: attraction between water molecules (H atom of one molecule and O atom of another)
Stronger Attraction: Solid, Liquid, Gas? Sec 2: Ionic and Covalent Bonding Ionic Bond Attraction between 2 oppositely charged ions
*Ions - charged atoms*
formed by transferring e-from a metal to a nonmetal
Ion Network Ionic compounds are in the form of networks, not molecules!!
A formula unit is the smallest ratio of ions in ionic compounds. Covalent Bond Attraction between neutral atoms formed by sharing e- between two nonmetals
Results in Molecules
Can be solid, liquid, or gas More than one Covalent Bond Atoms may share more than one pair of electrons
2 electrons shared: single bond
4 electrons shared: double bond
6 electrons shared: triple bond
The e- shared the stronger the bond Covalent Bonds Atoms do not always share electrons equally
nonpolar covalent bonds: bonds in which electrons are shared equally (usually same element bonding)
polar covalent bond: a bond in which there is an unequal sharing of electrons (two atoms of different elements sharing electrons)
Electronegativity Attraction an atom has for a shared pair of electrons.
Electrons tend to be more attracted to atoms of elements that are located farther to the right and closer to the top of the periodic table
higher e-neg atom s-
lower e-neg atom s+
Metallic Bonds a bond formed by the attraction between positively charged metal ions and the electrons around them
Metals are flexible and conduct electric current well because their atoms and electrons can move freely throughout a metal’s packed structure. Polyatomic Ions Compounds with both ionic and covalent bonds; groups of covalently bonded atoms that have either lost or gained electrons. (Have a + or – charge)
Act as a single unit; parentheses group the atoms of a polyatomic ion
Example: the formula for ammonium sulfate is written as (NH4)2SO4, not N2H8SO4.
Sec 3: Compound Names and Formulas Oxidation Number The charge on an ion.
Indicates the # of e- gained/lost to become stable. Ionic Nomenclature Write each ion, put the cation first
Don't show the charges in the final formula
Overall charge must equal zero!!
1. If charges cancel, just write the symbols.
2. If not, crisscross the charges to find subscripts.
3. Use parentheses when more than one polyatomic ion is needed.
4. Roman numerals equal the oxidation #. Cation: positive ion
Anion: negative ion Ionic Formulas Ionic Names 1. Write the names of both elements, cation (+) first.
2. Change the anion’s (-) ending to -ide.
3. Polyatomic ions have special names. (pg 190)
4. For transition metals, write the ox. # in parentheses using Roman numerals.
Calcium Oxide Ca 2+ O 2- Aluminum Chlorate Al 3- ClO 3 - Iron(III) Oxide Fe 3+ O 2- NaBr Na CO 2 3 FeCl 3 FeO Fe O 2 3 Molecular Nomenclature Covalent Names Prefix System
1. Less e-neg atom comes first.
2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element.
3. Change the ending of the second element to -ide. CCl 4 N O 2 SF 6 Arsenic trichloride
Tetraphosphorus decoxide Empirical formula - tells us the smallest whole-number ratio of atoms that are in a compound
Molecular formula - a chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of atoms Sec 3: Organic and Biochemical Compounds Organic Comounds A covalently bonded compound that contains carbon
Carbon atoms form four covalent bonds in organic compounds. Hydrocarbon A compound made of only carbon and hydrogen atoms
Alkanes: hydrocarbons that have only single carbon-carbon covalent bonds (# of H always double # of C CnH2n + 2)
Alkenes:hydrocarbons that have double carbon-carbon bonds.
Alkyne: hydrocarbons that have triple carbon-carbon bonds The carbon atoms in any alkane with more than three carbon atoms can have more than one possible arrangement.
Alcohol have hydroxyl, or –OH, groups
Example: methanol, CH3OH
Alcohols have the suffix -ol in their names.
Alcohol and water molecules behave similarly.
Neighboring alcohol molecules are attracted to one another. Polymers A molecule that is a long chain made of smaller molecules
Polymers have repeating subunits.
monomer: the smaller molecule that makes up the polymer
Polymers Some polymers are natural, and others are artificial.
natural polymers: rubber, starch, protein, and DNA
human-made polymers: plastics and synthetic fibers
A polymer’s structure determines its elasticity.
Polyethene is made of long chains.
It is flexible, but not elastic.
Polymers with connected chains (cross linking) are elastic.
They can stretch.
rubber bands Biochemical Compounds carbohydate: a class of molecules that includes sugars, starches, and fiber; contains carbon, hydrogen, and oxygen.
protein: an organic compound that is made of one or more chains of amino acids and that is a principal component of all cells
amino acid: a compound of a class of simple organic compounds that contain a carboxyl group and an amino group and that combine to form proteins
Biochemical Compounds DNA
DNA is a polymer that stores genetic information.
DNA is a very long molecule made of carbon, hydrogen, oxygen, nitrogen, and phosphorus.
It is in the form of paired strands.
It has the shape of a twisted ladder known as a double helix.
Most cells in your body have a copy of your genetic material in the form of chromosomes made of DNA.
DNA is the information that the cell uses to make proteins.