Chem Chapter 4 - Chemical Foundations: Elements, Atoms, Ions

Dalton's Atomic Theory

1. all atom of a given element are identical 2. the atoms of a given element are different from those of any other element 3. atoms of one elements can combine w/atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms 4. atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together

Rules for Writing Formulas

1. each atom present is represented by its element symbol 2. the number of each type of atom is indicated by a subscript written to the right of the element symbol. 3. when on only atom of a given type of element is present, the subscript 1 is not written

Ions

atoms acquire a charge by gaining or losing electrons either more or fewer electrons than protons.

Relative Atomic Mass

average mass of all the isotopes of an elements. (mass # x percentage)/100 + (mass # x percentage)/100

Nucleus

dense center of atom with positive charge, accounts for almost all atom's mass

Allotropes

different forms of the same element (ie solid carbon occurs in 3 forms: diamond, graphite, buckminsterfullerene)

Chemical Formulas

expresses the types of atoms and the number of each type of atom in each molecule of a given compound

Proton

found inside nucleus, positive charge, equal in magnitude to electron's negative charge Relative mass: 1836

Neutron

found within nucleus, no charge, slightly larger than proton Relative mass: 1838

Anion

ions with a negative charge, more electrons than protons, form by gaining electrons

Cation

ions with a positive charge, more protons than electrons, form by losing electrons

Atomic Number

number of protons

Atoms

tiny particles that make up elements

Formulas for Ionic Compounds

1. write the cation element symbol followed by the anion element symbol 2. the number of cations and anions must be correct for their charges to = 0 Ex: Mg2+ is combined w/Cl-. You will need 2 Cl- ions for every Mg2+ ion to balance the charges. The formula must be MgCl2

Ionic Bond

An ionic bond is formed between a metal and a non-metal. Non-metals(negative ion) are "stronger" than the metal(positive ion) and can get electrons very easily from the metal. These two opposite ions attract each other and form the ionic bond. (non metal and metal)

Isotopes

atoms of the same element w/the same number of protons, but different numbers of neutrons have the same atomic number, but different mass number

Ionic Compound

chemical compound where ions are held together in a structure by electrostatic forces termed ionic bonds. electrically neutral and the charges on the anions and cations in the compound must = 0 (ie: NaCl - Na = +1, Cl = -1, total charge = Na+Cl = +1+-1=0)

Diatomic Molecules

composed of 2 atoms of either the same or different chemicals (N, O, F, Cl, Br, I, H)

Covalent Bond

formed between two non-metals that have similar electronegativities. Neither atom is "strong" enough to attract electrons from the other. For stabilization, they share their electrons from outer molecular orbit with others (two non metals)

Electron

found outside the nucleus, negatively charged Relative mass: 1 part of atom that intermingles when atoms combine to form molecules # of these determine chemical behavior

Law of Constant Composition

given compound always has the same composition, regardless of where it comes from

Atom

has an overall charge of zero and must contain positive particles that balance exactly the negative charge carried by particles that we call electrons

Atomic Mass Number

number of protons and neutrons in the nucleus

Mass Number

protons+neutrons