Chem Ch 3
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hydrogen, oxygen, and water
- H2 is an explosive gas, O2 is a gas that is used for combustion, yet when the two are put together, we have H2O that forms a liquid that extinguishes flames and boils at hunderds of degrees above hydrogen or oxygen's boiling point.
- this shows how important it is to have compounds, because elements usually do not exist on their own.
- chemical bonds=result of interactions between the charged particles-electrons and protons- that compose atoms
- ionic bonds= M + NM. involves the transfer of electrons from one atom to another
- covalent bonds= NM + NM (2 or more) involves the sharing of electrons between two atoms
- metal + nonmetal
- metal loses e- (cation), nonmetal gains e- (anion)
- attracted by electrostatic forces
- in solid phase, it is shaped like a lattice (crystal)
- 2 or more nonmetals
- bond atoms by sharing electrons
- when negative charge lies between the two positive charges it has the lowest potential energy (most stable) b/c e- can interact with both protons.
- electron holds bond together by attracting the nuclei of both atoms
- "the shared electrons interact with the nuclei of both atoms, lowering the potential energy of the system through electrostatic interactions and forming a covalent bond."
representing compounds: chemical formulas and molecular models
- chemical formula=indicates the elements present in compound + relative # of atoms or ions of each
- more metallic (more positively charged) elements go first, less metallic (more negatively charged) elements follow.
types of chemical formulas
- empirical formula=relative # of atoms of each element in a compound e.g. CH2O for glucose
- molecular formula=actual # of atoms of each element in a molecule of a compound e.g. C6H12O6 for glucose
- molecular formula is always a whole number multiple of the empirical formula
- structural formula= uses lines to represent covalent bonds and show how atoms are connected. it gives a sense of the molecule's geometry. it can represent how many electrons are shared e.g. single(1 pair of e-), double(2 pairs of e-), triple bond(3 pairs of e- shared)
- ball-and-stick models= represent atoms as balls and chemical bonds as sticks; how the 2 connect reflects a molecule's shape; shows geometry of molecule
- space-filling molecular models=atoms fill the space between each other to more closely represent our best estimates for how a molecule might appear in reality; best sense of relative size and how atoms merge together in bonding
- the details about a molecule-atoms, length of bonds, angles of bonds, overall shape-determines the properties of the substance that the molecule composes
an atomic-level view of elements & compounds
- elements= atomic or molecular
- compounds=molecular or ionic
- atomic elements=exist in nature with single atoms as their basic unit
- molecular elements= exist in nature as molecules. most of these exist as diatomic molecules e.g. H2 . a few exist as polyatomic molecules e.g. P4, S8
- molecular compounds= 2 or more covalently bonded nonmetals e.g. H2O, CO2, C3H8
- ionic compounds= cations(usually metal) and anions(usually one or more nonmentals) bonded together by ionic bonds.
- formula unit= basic unit of ionic compound; the smallest, electrically neutral collection of ions. formula units are different from molecules in that they do not exist as discrete entities, but rather only as a part of a larger lattice (crystal)
- polyatomic ion=an ion composed of two or more atoms; e.g. ClO- the charge on the ion is a property of the whole ion, not just the oxygen atom.
ionic compounds: formulas & names
- ionic compounds occur throughout earth's crust as minerals e.g. limestone. they are also found in food we eat e.g. table salt, potassium chloride.
- ionic compounds tend to be very stable b/c attraction btwn cations +anions are strong. also, each ion interacts with several oppositely charged ions in the crystalline lattice
writing formulas for ionic compounds
- ionic compounds always contain + and - ions
- in a chemical formula, the sum of the charges of + ions (cations)= the sum of the charges of the - ions (anions)
- a formula reflects the smallest whole-number ratio of ions
naming ionic compounds
- identify if it's ionic compound (M+NM)
- two types of ionic compounds: metal forms only 1 type of ion or metal forms more than one type of ion
ions that form different charges
- Zn2+ Zinc
- Sc3+ Scandium
- Ag+ Silver
naming binary ionic compounds containing a metal that forms only one type of cation
- binary compounds= only 2 diff elements
- name of cation and base name of anion+ -ide
naming binary ionic compounds containing a metal that forms more than one kind of cation
- name of cation (charge in roman numerals) and base name of anion + -ide
- determine the charge of the metal cation by inference from the sum of the charges of the nonmetal anions-all must add up to zero.
naming ionic compounds containing polyatomic ions
- name of cation + name of polyatomic ion
- e.g. NaNO2 is sodium nitrite
- most polyatomic ions are oxyanions, anions containing oxygen and another element
- -ate = more oxygen
- -ite = less oxygen
- hypo- =less than
- per- = more than
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