Topic 3 - The structure of Atoms

matter, earth, water, air, fire, endlessly

Many ancient scholars believed __ was composed of the __ _ __ __ and . Divided into smaller and smaller pieces.

matter, matter, atomos

Democritus (460 - 360 B.C) was the first person to propose the idea that ____ was not infinitely divisible; instead _____ was made up of individual particles called _____

empty space

Aristole (484 - 322 B.C) disagreed with Democritus because he did not believe that _____ ______ could exsit

2,000

Aristotle’s views went unchallenged for _______ years until science developed methods to test validity of his ideas.

atom, chemical reactions

John Dalton revived the idea of the ____ in the early 18002 based on numerous ______ _____

Dalton’s atomic theory

_____ ______ ______ easily explained conservation of mass in a reaction as the result of thee combo, separation, or rearrangement of atoms

atom

The smallest particle of an element that retains the properties of the element is called the ______

scanning tunneling microscope (STM)

An instrument called the ___ _____ ______ allows individual atoms to be seen

cathode ray

when an electric charge is applied, a ray of radiation travels from the cathode to the anode.

steam, negative

Cathode ray are a ________ of particles carrying a __________ charge.

electrons

The particles carrying a negative charge are known as ____

J.J Thomson, charge-to-mass

__________ measured the effects of both magnetic and electric fields on the cathode ray to determine the ___________ ratio of a charged particle, then compared it to known values

less

The mass of the charged particle was much ____ than a hydrogen atom, then the lightest known atom

J.J Thomson, electron

_____- received the Nobel Prize in 1906 for identifying the first subatomic particle, the _____

Robert Millikan

In the early 1910s, ______ _______ used the oil-drop apparatus to determine the charge of an electron

1.602X10^-19, -1

Charges change in discrete amounts - ___________ coulombs, the charge of electron (now equaled to a single unit, ___)

neutral

Matter is ____

Plum pudding model

J.J. Thomson's _____ ________ ______ of the atom states that the atom is a uniform, positively changed sphere containing electrons.

positively

In 1911, Ernest Rutherford studied how _____ charged alpha particles interacted with solid matter.

A thin sheet of gold foil

By aiming the particles at a ____ _______ ______ _____ ____, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron.

bounced back

Although most of the alpha particles went through the gold foil, a few of them _________ _______, some at large angles.

empty space

Rutherford concluded that atoms are mostly _______ _______

nucleus

Almost all of the atom's positive charge and almost all of its mass is contained in a dense region in the center of the atom called the _________-

positively

Electrons are held within the atom by their attraction to the _____ charged nucleus.

protons

3rd Model of the Atom – Nuclear Model 1913 Rutherford refined the model to include positively charged particles in the nucleus called

_______-

neutrons

James Chadwick received the Nobel Prize in 1935 for discovering the existence of _________, neutral particles in the nucleus which accounts for the remainder of an atom’s mass.

the electron, the proton, and the neutron.

All atoms are made of three fundamental

subatomic particles: ______ _______ _______

spherically

Atoms are ________ shaped.

nucleus

Atoms are mostly empty space, and electrons travel around the _____ held by an attraction to the positively charged nucleus.

quarks

Scientists have determined that protons and neutrons are composed of subatomic particles called _____

nucleus

Each element contains a unique positive charge in their ______-

atomic number.

The number of protons in the nucleus of an atom identifies the element and is known as the element’s ______ ________

neutrons

All atoms of a particular element have the same number of protons and electrons but the number of _______ in the nucleus can differ.

isotopes.

Atoms with the same number of protons but different numbers of neutrons are called ______

constant.

The relative abundance of each isotope is usually _______

mass

Isotopes containing more neutrons have a greater ______

chemical

Isotopes have the same ____ behavior.

mass number

The _____ ______ is the sum of the protons and neutrons in the nucleus.

atomic mass unit

One ______ ________ _______ (amu) is defined as 1/12th the mass of a carbon-12 atom.

proton, neutron

One amu is nearly, but not exactly, equal to one _____ and one _______

atomic mass

The ______ ______- of an element is the weighted average mass of the isotopes of that element.

Nuclear reaction

_________ _______ can change one element into another element.

radioactivity.

In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called

radiation.

The rays and particles emitted are called

nuclear reaction

A reaction that involves a change in an atom's nucleus is called a ______ _______

radioactive decay.

Unstable nuclei lose energy by emitting radiation in a spontaneous process called ____________ ___________

nonradioactive

Unstable radioactive elements undergo radioactive decay thus forming stable __________elements.

alpha particles.

Alpha radiation is made up of positively charged particles called ________ _______-

two, two

Each alpha particle contains _____ protons and _____- neutrons and has a 2+charge.

radioactive decay

The figure shown below is a nuclear equation showing the ______ _______ of radium-226 to radon-222.

Beta radiation

_____ _______ is radiation that has a

negative charge and emits beta particles

beta particle

Each _____ _______- is an electron with a 1– charge.

Gamma rays

_____ _______- are high-energy radiation with no mass and are neutral.

most

Gamma rays account for ___ of the energy lost during radioactive decay

unstable

Atoms that contain too many or two few neutrons are _____ and lose energy through radioactive decay to form a stable nucleus.

few

_______ exist in nature—most have already decayed to stable forms.