Chem Test 2 chpt 4

proton (p+)

- positively charged subatomic particle - mass is 1 amu (1.67262 x 10-27 kg)

neutron (n0)

- subatomic particle with no charge (neutral) - mass is same as that of a proton (1 amu) (1.67493 x 10-27 kg)

Group B elements

- transition metals - inner transition metals

atomic mass unit (amu)

- unit created to compare the masses of atoms - equal to the mass of 1 proton (or 1 neutron) - defines as 1/12th the mass of a carbon atom (with 6 protons and 6 neutrons)

periodic law

- when elements are arranged in order of increasing atomic number there is a periodic repetition of their physical and chemical properties - elements with similar properties end up in the same column

Dalton's Atomic Theory

1) All elements are composed of tiny indestructible particles called atoms. 2) Atoms of the same element are identical (same mass and other properties). The atoms of any one element are different from those of any other element. 3) Atoms combine in simple whole-number ratios to form compounds.

Nuclear Theory of the Atom (proposed by Rutherford)

1. Most of an atom's mass and all of its positive charge are contained in a small core called the nucleus. 2. Most of the volume of the atom is empty space through which the tiny, negatively charged electrons are dispersed. 3. There are as many negatively charged electrons outside the nucleus as there are positively charged particles (protons) inside the nucleus, so that the atom is electrically neutral.

goes against what Dalton said)

atoms - can be broken down into smaller fundamental particles

cations

- positively charged ions (Li+)

Ernest Rutherford

(1871- 1937) - worked under Thompson - proved plum pudding model wrong

periods

- 7 horizontal rows - properties of elements change as you move across a period - patterns of properties repeat from period to period

groups

- AKA families - vertical columns - elements have similar physical and chemical properties - each group is identified by a number and the letter A or B

Group A elements

- AKA representative elements or main-group elements - made up of Groups 1A through 7A and Group 0

J. J. Thompson

- English physicist (1856-1940) - discovered electron within atoms (a negatively-charged particle smaller and lighter than an atom) - suggested the plum pudding model of the atom (negatively charged electrons were small particles held within a positively charged sphere)

John Dalton

- English schoolteacher (1766 - 1844) - came up with the atomic theory

Dmitri Mendeleev (1834-1907)

- Russian chemist who created the first periodic table - arranged elements by increasing atomic mass

electron (e-)

- negatively charged subatomic particle - mass is 1/1840 that of a proton (1/1840 amu) (0.00091 x 10-27 kg)

metalloids

- occupy the zigzag border between metals and nonmetals - properties are intermediate between metals & nonmetals

atomic number also

- also tells you the number of electrons

nucleus

- central core of an atom - composed of protons and neutrons (electrons surround the nucleus) - contains most of the atom's mass (99.9%)

ion

- charged particle formed when an atom gains or loses electrons in chemical reactions

Henri Moseley (1887-1915)

- created a periodic table arranging the elements in order of increasing atomic number (instead of atomic mass) - this is how we arrange the table today

Rutherford's experiment:

- directed tiny, positively charged particles (alpha-particles) at a sheet of gold foil - expected the particles to pass right through the gold foil (if the plum pudding model were true and the charges in the gold atom were spread throughout the entire volume of the atom) - results: most particles passed directly through but were deflected and some bounced back - conclusion: matter must have large regions of empty space dotted with small regions of dense matter the mass and positive charge of an atom must be concentrated in a space smaller than the atom

The nature of electrical charge:

- electrical charge is a fundamental property of protons and electrons - positive and negative charges attract each other - positive charges repel positive charges and negative charges repel negative charges - positive and negative charges cancel each other (a paired proton and electron are charge-neutral)

metals

- found on left side of table (except for hydrogen) - conduct electricity - shiny - ductile - can be drawn into wires - malleable - can be hammered into thin sheets all are solid at room temperature (except 1) - tend to lose electrons when they undergo chemical changes

chemical symbol

- one or two letter abbreviation for each element (if 2 letters, only first letter is capitalized!!)

valence electrons

- outermost electrons in an atom - take part in chemical bonding - for Group A elements, the group number gives you the number of valence electrons

Democrites

Greek philosopher (460-370 BC) - theorized that matter was composed of tiny, indestructible particles called atoms

- Group 1A

alkali metals

- Group 2A

alkaline earth metals

periodic table

arrangement of the atoms according to similarities in their properties

isotopes

atoms with the same number of protons but different numbers of neutrons same atomic numbers but different mass numbers - chemically alike because they have the same numbers of protons and electrons which are responsible for chemical behavior

atoms

building blocks of all matter - compose everything around us - their properties determine matter's properties atom - smallest identifiable unit of an element - smallest particle of an element that keeps the properties of that element

modern periodic table

elements listed in order of increasing atomic number from left to right and top to bottom contains each element's symbol, name, atomic number and atomic mass

nonmetals

found in the upper right corner - poor conductors - nonlustrous - some are gases at room temperature - others are brittle solids - tend to gain electrons when they undergo chemical changes

Group 7a

halogens

plum pudding mode

negatively charged electrons were small particles held within a positively charged sphere)

anions

negatively charged ions (F-)

matter - usually charge

neutral

atoms are electrically neutral:

number of protons equals the number of electrons

building blocks of the atom

proton, electron, neutron

natural atoms/elements

there are about 91 different natural atoms (because there are about 91 natural elements)

mass number

total number of protons and neutrons in an atom

atomic mass

weighted average of the mass of the atoms in a naturally occurring sample of an element