Chemistry Unit 2

What are two things about matter that ancient scientists believed?

1. Matter was composed of such things as earth, water, air, and fire.

2. Matter could be endlessly divided into smaller and smaller pieces.

Greek Philosophers Democritus vs Aristotle

Democritus: 1st person to propose the idea that matter was not infinitely divisible, and was made up of individual particles called atomos (atoms).

Aristotle: disagreed w/ Democritus because he didn’t believe empty space could exist.

Characteristics of matter according to Democritus

• Solid

• Homogeneous

• Indestructible

• Indivisible

How long did Aristotle’s vies go unchallenged for?

About 2000 years

John Dalton

Modernized the idea of the atom in the early 1800s based on numerous chemical reactions.

Dalton’s Atomic Theory

The conservation of mass in a reaction is the result of the combination, separation, or rearrangement of atoms.

Characteristics of atoms according to Dalton

• Indivisible & Indestructible

• Atoms of a specific element are different from those of another element

• Different atoms combine in whole-number ratios to form compounds

Atom

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

Scanning tunneling microscope (S.T.M)

Allows individual atoms to be seen.

Cathode Ray

Stream of particles carrying electrons.

JJ Thomson

Won the Nobel Prize in 1906 for identifying the first subatomic particle— the electron.

Robert Millikan

Used the oil-drop apparatus to determine the charge of an electron.

Millikan’s equation of the mass of an electron

9.1 × 10^-28 = 1/1840 the mass of a hydrogen atom

JJ Thomson’s Plum Pudding

States that the atom is a uniform, positively charged sphere containing electrons.

Ernest Rutherford Gold Foil Experiment

Since the some of the alpha particles bounced back from the gold foil, he determined that 1. atoms are mostly empty space, and 2. the atoms’ positive charge most of its mass is contained in its center, the nucleus

Why did the alpha particles deflect in Rutherford’s Gold Foil Experiment

Because of the repulsive force between the positively charged nucleus and the positive alpha particles

Ernest Rutherford changes to the model of the atom

Included protons in the nucleus

James Chadwick

Won the Nobel Prize in 1935 for his discovery of neutrons

How do electrons travel around the nucleus

By their attraction to the nucleus’ positive charge

Protons and neutrons are composed of subatomic particles called _______

quarks.

What subatomic particle correlates to the atomic number of an element?

# of Protons.

Mass number

Sum of protons and neutrons.

Isotopes

Atoms with the same number of protons and different number of neutrons.

One atomic mass unit (amu) is defined as what?

1/12th of the mass of a carbon-12 atom.

Atomic mass

Weighted average mass of the isotopes of an element.

What type of reactions can change one element into another element?

Nuclear reactions.

Radioactivity

When substances spontaneously emit radiation.

Nuclear reactions involve a change in what part of the atom?

The atom’s nucleus

Radioactive Decay

When unstable nuclei lose energy by emitting radiation, forming a stable one.

Alpha Radiation

When an atom undergoes radioactive decay and emits an alpha particle.

What subatomic particles does an alpha particle contain? What charge does it have?

2 protons and 2 neutrons; It has a 2+ charge.

Beta radiation

Radiation that emits negatively charged particles called beta particles.

What charge do beta particles have?

They are electrons/positrons with a positive charge

Gamma Radiation

Radiation where a photon of energy is emitted from an unstable nucleus

Gamma rays have no _____ and no _____

mass; charge.

_________ rays account for most of the energy lost during radioactive decay

Gamma

Atoms that contain too many or too few neutrons are ________ and _____ energy through radiactive decay to form a stable nucelus.

unstable; lose.

Why are radioactive elements rare in nature?

Because most of them have already decayed to a stable form.

An element’s chemical behavior is related to the ________ of _______ in its atoms

arrangement; electrons.

Electromagnetic Radiation

A form of energy that exhibits wave-like behavior as it travels through space.

Wavelength

The shortest distance between equivalent points on a continuous wave.

Frequency

The number of waves that pass a given point per second.

Amplitude

The wave’s height from the origin to a crest.

Equation for the speed of light

3.00 × 10^8 m/s

What to components produce the speed of light?

Wavelength and Frequency.

What natural phenomenon contains a continuous range of wavelengths and frequencies?

Sunlight

Prism

Separates sunlight into a continuous spectrum of colors.

Electromagnetic spectrum

Includes all forms of electromagnetic radiation.

Matter can gain or lose energy in small, specific amounts called: ________

quanta.

Quantum

The minimum amount of energy that can be gained or lost by an atom.

Value of Planck’s Constant

6.626 × 10^-34 J x s

The Photoelectric Effect

When electrons are emitted from a metal’s surface when light of a certain frequency shines on it.

In 1905, Albert Einstein proposed what?

The idea that light has a dual nature.

A beam of light has what two properties?

Wavelike & particlelike

Photon

A massles particle of electromagnetic radiation that carries a quantum of energy.

Photon Equation

Ephoton = hv

Where h = Planck’s constant and v = frequency

The Atomic Emission Spectrum

The set of frequencies of the electromagnetic waves emitted by the atoms of an element.

Who correctly predicted the frequency lines in hydrogen’s atomic emission spectrum?

Neil Bohr.

Ground state

The lowest allowable energy state of an atom.

What state is an atom in when it gains energy?

An excited state.

What is the quantum number for the ground state of an electron?

n = 1; As energy is added, the quantum number increases.

T or F: Electrons move around the nucleus in circular orbits.

False

Louis de Broglie hypothesized that electrons have what kind of behaviors?

Wave-like behaviors.

The de Broglie equation

wavelength = Planck’s constant/ mass (of particle) x velocity

Heisenberg proved what fact about objects?

That it is impossible to take any measurement of an object without disturbing it.

Heisenberg Uncertainty Principle

It is impossible to know precisely the velocity and position of a particle simultaneously.

Three dimension region around an atom’s nucleus

Atomic orbital

Principal Quantum Number (n)

Indicates the relative size and energy of atomic orbitals.

N specifies the atoms’ what?

Principal energy levels.

Energy sublevels

Are contained within the principal energy levels.

Each orbitals have what difference?

Difference in shape.

Electron configuration

The arrangement of electrons in an atom

Aufbau Principle

States that each electron occupies the lowest energy orbital avaialble

Pauli Exclusion Principle

States that a maximum of two electrons can occupy a single orbital, only if the electrons have opposite spins.

Hund’s Rule

States that single electrons with the same spin must occupy each equal energy orbital before additional electrons with opposite spins can occupy the same energy level orbitals.

Valence electrons

Electrons in the atom’s outermost orbitals.