Chapter 4 Pg. 100-118

Ancient Greek Models of Atoms

• __________ – thought that all substances were built up from only ____ elements: earth, air, fire, and water – matter could be divided an unlimited number of times • __________ – believed that all matter consisted of extremely _____ particles that could not be divided – called particles

atoms

from the Greek word ________, which means “uncut” or “indivisible”

Dalton’s Atomic Theory

• ____________ - born in England in 1766 – Teacher – Interest in predicting the _______, led to his study of the behavior of gases in air -- Correctly concluded that a gas consists of _________ _________

Dalton’s Atomic Theory

•

Evidence for Atoms

– Measured the ______ of elements that combine when compounds form.

– Noticed that no matter how _______ or _____the sample, the ratio of the masses of the elements in the compound is always the same (aka fixed composition)

Dalton’s Atomic Theory

• •

________ Theory

- Dalton proposed the theory that all matter is made up of individual particles called ______, which cannot be divided.

Main Points of Theory

1. All elements are composed of ______.

2. All atoms of the same element have the same mass, and atoms of ________ elements have different masses.

Dalton’s Atomic Theory

• •

Main Points of Theory continued…

3. __________ contain atoms of more than one element.

4. In a particular compound, atoms of different elements always combine in the _____ _____ Not all of Dalton’s ideas about atoms were completely ______, but scientists did not discard his theory, they revised it to take into account new discoveries

Dalton’s Atomic Theory

Thomson’s Model of the Atom

• • • When rubbed, some materials gain the ability to ______ or _____other materials.

Based on their ________, they are said to have either positive or negative electric charges.

Objects with ___ charges repel or push apart.

Thomson’s Model of the Atom

• Objects with ________ charges attract, or pull together.

• Some charged particles can flow from one location to another. A flow of charged particles is called an

________ _______

Thomson’s Model of the Atom

• J.J Thomson used _______ current to learn more about atoms

Thomson’s Model of the Atom

• Thomson’s Experiment (pg. 102) – __________ that the beam was a stream of charged particles that interacted with the air in the tube and cause the air to glow.

– Placed charged _____ plates at either end-> caused beam to deflect or bend – Observed beam: ________ by negatively charged plate and attracted by positively charged plate

Thomson’s Model of the Atom

• Evidence for Subatomic Particles – Concluded that the particles in the beam had a _________ charge because they were attracted to the positive plate.

– Thomson’s experiments provided the _____ evidence that atoms are made of even ______ particles.

– Revised Dalton’s model to account for the ________ particles

Thomson’s Model of the Atom

• Thomson’s Model – Atom is ______: meaning it has neither a negative nor a positive charge – Negative charges were evenly ________ throughout an atom filled with a positively charged mass of matter – “______ _______” model (may want to think of chocolate chip ice cream)

Thomson’s Plum Pudding Model

Rutherford’s Atomic Theory

• _____, Rutherford discovered that uranium emits fast moving particles that have a positive charge called

_____ ________

Rutherford’s Atomic Theory

• Hypothesis : (asked student- _______, to find out what happens to alpha particles when they pass through a thin sheet of gold) Predicted that most particles would travel in a _______ path from their source to a screen that lit up when struck.

Rutherford’s Atomic Theory

• The _______ ______ Experiment – Aimed narrow beam of alpha particles at gold, the material around the ______ produced a flash of light when struck by fast-moving alpha particles – Could figure out ____ of alpha particles by observing the flash after they had passed through the gold – Did _____ support Rutherford’s prediction

Rutherford’s Atomic Theory

• Gold Foil Experiment continued… – More particles were deflected than he expected – About 1 out of every ______ was deflected by more than 90 degrees – Some alpha particles behaved as though they had struck an object and bounced _______ back

Gold Foil Experiment

Rutherford’s Atomic Theory

• Discovery of the Nucleus – Alpha particles whose paths were ________ must have come close to another charged object – The closer they came, the greater the deflection – _________: the positive charge of an atom is not evenly spread throughout the atom, it is concentrated in a very small central area- ______ –

Nucleus

: a dense, positively charged mass located in the center of the atom

Rutherford’s Atomic Theory

• According to Rutherford’s model, all of an atom’s _______ charge is concentrated in its nucleus

Chapter 4 Section 2 Pg. 108-112

Properties of Subatomic Particles

• • Protons, electrons, and neutrons are _________ particles

Protons:

– A __________charged subatomic particle that is found in the nucleus of an atom – Positive charge (amount varies among elements), each proton is _____ – Each _________ must contain at least one particle with a positive charge

Properties of Subatomic Particles

•

Electrons

– Comes from Greek word meaning “______” – A _________ charged subatomic particle that is found in the space outside the nucleus – Each electron has a charge ____

Properties of Subatomic Particles

•

Neutrons

– 1932, English physicist J. _________ designed an experiment to show that neutrons exist; concluded particles were ________ because a charged object did not deflect their path – A neutral subatomic particle that is found in the nucleus of an atom – ______ is almost exactly equal to that of a proton

Comparing Subatomic Particles

• • • • Protons, electrons, and neutrons can be distinguished by _____, charge, and location in an atom.

Protons and neutrons have almost the _____ mass It would take about 2,000 electrons to equal the mass of one proton Protons and neutrons are _______ nucleus, electrons are in outside space

•

Atomic Number and Mass Number

______ predicted that the atoms of any element are different from the atoms of all other elements •

Atomic Number

– atoms of any given element always have the same number of protons – Atomic number of an _______ equals the number of protons in an atom of that element – _______ of different elements have different numbers of protons

Atomic Number and Mass Number

•

Mass Number

– the mass number of an atom is the ____ of the protons and neutrons in the nucleus of that atom.

– Ex: an atom of Al with 13 protons and 14 neutrons has a mass number of 27 Atomic mass is the same as mass number

Isotopes

• • • Every atom of a given element _____ _____have the same number of neutrons.

Isotopes

are atoms of the same element that have different numbers of neutrons and different mass numbers

Isotopes of an element have the ____ atomic number but different mass numbers because they have different number of neutrons

M o d e r n A t o m i c T h e o r y

• •

Bohr’s Model of the Atom

Bohr was a ______ physicist who worked with Rutherford Bohr _______ with Rutherford’s model, but Bohr’s model focused on the electrons •

Energy Levels

– In Bohr’s model, _________ move with constant speed in fixed orbits around the nucleus (like planets around a sun)

Bohr’s Model of the Atom

•

Energy Levels

– Each ________ in an atom has a specific amount of energy – If an atom _____ or ______energy, the energy of an electron can change – The possible energies that electrons in an atom can have are called

______ _______

– An electron cannot exist between energy levels

Bohr’s Model of the Atom

• •

Energy Levels

– An electron in an atom can _____ from one energy level to another when the atom gains or loses energy – The _____ of the jump between energy levels determines the amount of energy gained or lost

Evidence for Energy Levels

– Scientists can measure the energy _______ or released when an electron absorbs or releases energy and moves to higher or lower energy levels

Bohr’s Model of the Atom

Electron Cloud Model

• • • An

electron cloud

is a ______ model of the most likely locations for electrons in an atom The cloud is _______ at those locations where the probability of finding an electron is high Scientists use the electron cloud model to describe the possible _______ of electrons around the nucleus

Atomic Orbitals

• • • The ______ _____ represents all the orbitals in an atom An

orbital

is a region of space around the nucleus where an ______ is likely to be found

An electron cloud is a good approximation of how electrons behave in their orbitals

Atomic Orbitals

• • • Level which an electron has the ____ energy– the lowest energy level– has only one orbital Higher energy levels have _____ than one orbital Each orbital can contain _____ electrons at most

Electron Configurations • • • An

electron configuration

is the __________ of electrons in the orbitals of an atom

The most ______ electron configuration is the one in which the electrons are in orbitals with the _______ possible energies

When all the electrons in an atom have the _______ possible energies, the atom is said to be in its

ground state

Electron Configurations • • • If a lithium atom ______ enough energy, one of its electrons can move to an orbital with a higher energy, this ____________ is referred to as an

excited state

An

excited state

ground state is _____ stable than the Eventually the electron _____ _______and the atom returns to the ground state

Electron Configuration • Helium, neon, argon, krypton, and xenon atoms _________ from excited states to the ______ state emit the light you see in “neon” lights