CK-12 Chemistry Atomic Structure

isotope

Isotopes are atoms that have the same atomic number, but different mass numbers due to different number of neutrons.

Plum Pudding Model

J.J Thomsons model of an atom, in which he thought electrons were randomly distributed within a positively charged cloud; The "plum pudding" model of the atom consisted of a uniform sphere of positive charge with negative electrons embedded in the sphere.

atomic mass

the weighted average of the masses of the naturally occurring isotopes of an element

Gold Foil Experiment

- Ernest Rutherford discovered the nucleus - Bombardment of gold foil with alpha particles showed that a very small percentage of alpha particles were deflected. The nuclear model of the atom consists of a small and dense positively charged interior surrounded by a cloud of electrons.

John Dalton

- developed modern atomic theory -John Dalton determined a number of atomic weights of elements in the early 1800s. Atomic weights were the basis for the periodic table that Mendeleev developed.

Dalton's Atomic Theory

1) elements are composed of atoms. 2) atoms of same element are identical, but differ from other elements. 3) elements can mix together 4) atoms only change when mixed with other elements.... -All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties. Atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements can combine in simple whole number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged

compound

A compound is a substance that contains two or more elements chemically combined in a fixed proportion.

Atom

Atoms are the building blocks of matter. They are the smallest particles of an element that still have the element's properties. All atoms are very small, but atoms of different elements vary in size. Three main types of particles that make up all atoms are protons, neutrons, and electrons.

Atomic Mass Unit

Carbon-12 is the reference for all atomic mass calculations. An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12. The mass of an atom is affected by the interactions of particles within the nucleus.

isotope

Frederick Soddy (1877-1956) gave important clues about the internal structure of atoms. coined the term isotope His work showed that some substances with different radioactive properties and different atomic masses were in fact the same element.

Aristotle

Greek philosopher; According to Aristotle, everything was composed of four elements: earth, air, fire, and water.

Democritis (400 BC)

He taught that there were substances called atoms and that these atoms made up all material things. The atoms were unchangeable, indestructible, and always existed.

atomic model

Model that shows the structure of an atom and the arrangement of subatomic particles in an atom.

Atomic nucleus

Rutherford proposed a model of the atomic nucleus which had a solid core. - a strong nuclear force holds the protons and neutrons together in the nucleus of the atom. -An atom's dense central core, containing protons and neutrons.

Calculating Average Atomic Mass

The SUM of: the Percent abundance of each isotope/100 x mass of the isotope ..The atomic mass of an element is the weighted average of the atomic masses of the naturally occurring isotopes of that element. Calculations of atomic mass use the percent abundance of each isotope.

law of definite proportions

The law of definite proportions states that a given chemical compound always contains the same elements in the exact same proportions by mass.

law of multiple proportions

The law of multiple proportions states that whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

mass number

The mass number = number of neutrons + atomic number. -The mass number is defined as the total number of protons and neutrons in an atom.

nuclide

The nucleus of a given isotope of an element; and atom that is defined by the number of protons and neutrons in its nucleus.

nuclide

general term for any isotope of any element

isotopes

atoms of the same element that have the same number of protons but different numbers of neutrons

electron

definition: a negatively charged subatomic particle outside the nucleus; The electron was discovered using a cathode ray tube...An electric current was passed from the cathode (the negative pole) to the anode (positive pole).

proton

definition: a positively charged subatomic particle Eugene Goldstein (1850-1930) discovered evidence for the existence of this positively charged particle; called these canal rays

neutron

definition; a subatomic particle with no charge -Chadwick was able to show that the neutron has essentially the same mass as a proton, but with no charge.

law of conservation of mass

during a chemical reaction, the total mass of the products must be equal to the total mass of the reactants. In other words, mass cannot be created or destroyed during a chemical reaction, but is always conserved.

cathode ray tube

in which an electric current was passed through gases at low pressure. -invented by Sir William Crookes. Experiments showed that the rays had mass.

cathode rays

rays of electricity that flow from the cathode to the anode. J.J. Thomson proved that these rays were actually negatively charged subatomic particles (or electrons).

atom

smallest particle of an element that retains the properties of that element.

Atomic number

the number of protons in the nucleus The number of electrons is equal to the number of protons in an atom of an element.

atomic number

the number of protons in the nucleus of an atom

nucleus

the small central core of the atom where most of the mass of the atom (and all of the atoms positive charge) is located

mass number

the total number of protons and neutrons in the nucleus of an atom

atomic mass unit

used to express atomic and molecular masses, it is the approximate mass of a hydrogen atom, a proton, or a neutron and is one-twelfth of the mass of an unbound carbon-12 atom at rest; it is equivalent to the dalton