Chapter 4

Elements and the Periodic Table8th Grade Science

Introduction to Atoms

• Greek philosopher named __________ - proposed that matter is made up of tiny particles that cannot be made any smaller

• ________ - means “uncuttable”• _____ - smallest particle of an element• ___________ - formed in the 1600’s as a

series of models developed from experimental evidence.

Democritus

“Atomos”

Atom

Atomic Theory

Atomic Theory

• As more experiments were conducted and evidence collected, the theory and models were revised.

• ________________ - John Dalton, English chemist, inferred that atoms had certain characteristics.

• Dalton’s atomic theory is still accepted today!• Atoms were like smooth, hard balls that cannot

be broken down

Dalton’s Atomic Theory

Summary of Dalton’s Ideas page 103

• All elements are composed of atoms that cannot be ______.

• All atoms of the same element are exactly alike and have the same ____.

• An atom of one element cannot be _________ into an atom of a different element – only rearranged.

• Every ________ is composed of atoms of different _________ combined in a specific ________.

divided

masschanged

compoundelements

ratio

Thomson Model

• ___________ - 1897 atoms have negatively charged electrons embedded in a positive sphere.

• _______ - negatively charged particles

JJ Thomson

electrons

Rutherford and the Nucleus

• 1911 - ____________ - a student of Thomson, found evidence that contradicted Thomson’s model.

• ______________ - beam of positively charged particles aimed at a thin sheet of gold foil. Most of the particles passed through the foil as expected. However, a few particles were _______.

Ernest Rutherford

Gold Foil Experiment

deflected

Conclusions from the Foil Experiment

• Since like charges _____ each other, Rutherford concluded that an atom’s _________ charges must be clustered in the _____ of the atom.

• ______ - center of the atom • ________ - no mass• ________ - positively charged particles that

have mass and are located in the nucleus of the atom.

repel

positivecenter

nucleus

electrons

protons

Rutherford’s Model

Bohr’s Model

• ___________ - 1913, Danish Scientist, student of both Thomson and Rutherford – electrons move around the nucleus in certain _____ based on energy levels.

• Bohr’s Model resembles planets orbiting the sun or layers of an onion.

Neils Bohr

orbit

Cloud of Electrons

• 1920’s – atomic model changed again• Scientists determined that electrons DO NOT

orbit the nucleus like planets.• _________ can be anywhere in a cloudlike region

around the __________.• An _______ movement is related to its

_________ - specific amount of energy that it has.• ____________ affects the atoms reactions with

other atoms.

Electronsnucleus

electronsEnergy level

Energy level

The Modern Atomic Model

• ___________ discovered another particle in the nucleus of atoms.

• _________ - particle discovered by Chadwick that has no electrical charge and nearly the same mass as _______.

• _______________ - consists of a nucleus that contains protons and neutrons surrounded by a cloudlike region of moving electrons.

James Chadwick

Neutrons

Protons

Modern Atomic Model

Particle Charges

• In an tom the number of ________ equals the number of __________.

• _________ have a positive charge and a ____• _________ have a negative charge and very

little _______.• _________ have neutral charge and a mass that

equals that of protons.• ________ charge of ________ equals the

________ charge of _________.

protonsElectrons

Protons mass

electronsmass

Neutrons

Positive Protonsnegative Electrons

Masses and ChargesParticle Symbol Charge Relative

Mass (amu)

Proton p⁺ 1₊ 1

Neutron n 0 1

Electron e⁻ 1₋ 1/1,836

• Charges balance making the atom neutral

• Number of neutrons does not have to equal the number of protons

• Neutrons do not affect the charge of an atom because they have no charge

• Approximately 2,000 e⁻ equal mass of one proton.

Atomic Number

• Every atom of an element has the same number of _________.

• _____________ - number of protons in the nucleus of an atom.

• Atomic number identifies an _________.• _______ - atoms with the same number of

protons but a different number of neutrons.• __________-sum of the protons and neutrons

in the nucleus of an atom.

protonsAtomic Number

element

Isotopes

Mass number

Patterns in the Elements

_____________ - Russian scientist discovered a set of patterns that applied to all elements.

Mendelev arranged the elements in order of increasing __________.

____________ - organization of the elements where the properties of the elements repeat in each row of the table.

___________ - Brittish scientist discovered a way to measure the positive charge on an atom’s nucleus – the atomic number.

Dmitri Mendelev

Atomic massPeriodic table

Henry Moseley

Periodic Table of Elements

• After Moseley’s discovery, the periodic table was rearranged from ________ to _________.

• Properties of an element can be predicted based on its place in the ___________.

• Periodic table is arranged according to ___________ increasing from left to right.

• ________ - horizontal rows on the periodic table where the properties of the elements change in a set pattern.

Atomic mass Atomic number

Periodic table

Atomic number

periods

Organization of the Periodic Table

• Elements on the left side of the periodic table are _______________.

• Elements in the middle of the periodic table are ______________.

• Elements on the right side of the periodic table are _________________.

• ______ - 18 vertical columns or “families” on the periodic table with similar characteristics such as rate of reaction. (except lanthanides and actinides).

Highly reactive metals

Less reactive metals

Metalloids and non-metals

Groups

Reading the Periodic Table

• Each element in the periodic table has all of the following:– ____________ - number of protons in the nucleus– _____________ - 1 or 2 letter representation– ____________ – __________ - average mass of all of the isotopes

of the element.

Atomic NumberChemical Symbol

Element Name

Atomic Mass

Metals

• Physical properties of metals:– ________– __________ - material can be hammered or rolled

into flat sheets and other shapes.– _______ - material can be pulled out or drawn into

a thin wire– __________ - ability of an object to transfer heat or

electricity to another object.– ___________ - metal that is liquid at room

temperature

shininessmalleability

ductility

conductivity

Mercury (Hg)

Chemical Properties of Metals

• _________ - the ease or speed of an element to combine or react to other elements and compounds.

• Metals usually react by losing ________ to other atoms.

• Sodium (Na) is very reactive where gold (Au) and platinum (Pt) are much less reactive.

• __________ - the destruction of a metal because of its reactivity.

reactivity

elements

corrosion

Metals in the Periodic Table

• _______ of metals decreases from left to right on the periodic table.

• ____________ - metals in Group 1 on the periodic table that react with other elements by losing one ______.

• Alkali metals are never found in __________ elements in nature – only in compounds.

• ___________________ - two most important alkali metals – important for life processes.

reactivity

Alkali Metals

electron

uncombined

Sodium(Na) and potassium (K)

Alkali Earth Metals

• ______________ - Group 2 on the periodic table that react with other metals by losing two electrons.

• Not as reactive as metals in __________ but more reactive than ,most other metals.

• Never found uncombined in nature.• ______________________ - two most

common alkali earth metals.

Alkali Earth Metals

Group 1

Magnesium (Mg) and Calcium (Ca)

Other Elements on the periodic table

• ____________ - elements in Group 3 through 12. These metals are hard and shiny, good conductors of electricity, less reactive than metals in Groups 1 and 2. ________ is an example of a very important transition metal.

• _______________ - only some are metals such as aluminum, tin and lead

• _________ - two rows of elements at the bottom of the periodic table.

Transition Metals

Iron (Fe)

Groups 13, 14, and 15

Lanthanides

Lanthanides

• __________ - soft, malleable shiny metals with high conductivity.

• Lanthanides mix with other metals to form _____.

• _____ - mixture of a metal and at least one other element, usually another metal.

• _________ - only four occur naturally on earth – all others were created artificially. These elements are VERY unstable. Ex. Uranium

Lanthanides

alloys

alloy

Actinides

Synthetic Elements

• ____________ - elements that follow uranium that are not found naturally on Earth – when nuclear particles are forced to crash into one another.

• _____________ - powerful machines used by scientists to move atomic nuclei to very high speeds.

Synthesized

Particle accelerator

Non-metals and Metalloids

• Physical properties of non-metals:– ______________– _____________________– ______________– Many non-metals are common elements on Earth– ________non-metals are ______ at room

temperature.– ___________ - only non-metal that is liquid at

room temperature

Poor conductors

Reactive with other elements

Dull and brittle

10 of 16 gases

Bromine (Br)

Chemical Properties of Non-Metals

• Atoms of non-metals usually _____ or ______ electrons with atoms that they react with.

• When metals and non-metals react, _________ move from the metal atoms to the non-metal atoms.

• Non-metals can also form compounds with other non-metals.

gain share

electrons

Families of Non-metals

• 1. _______________ - Group 14 only carbon is a non-metal. atoms that gain, lose, or share ____electrons when reacting with other elements.

• 2. ______________ - Group 15 contains two non-metals, nitrogen and phosphorous. These atoms usually gain, lose or share _______ electrons when reacting with other elements.

• 80% of the atmosphere is nitrogen gas (N₂)

The Carbon Family

four

The Nitrogen Family

three

Families of Non-Metals continued

• 3. _____________ - Group 16 contains three non-metals – oxygen, sulfur and selenium. Elements in the oxygen family usually gain or share ___ electrons.

• _________ is highly reactive – it can combine with nearly any other element.

• Oxygen is the ____ most abundant element in the atmosphere (Nitrogen is first)

The Oxygen Family

two

oxygen

most

The Halogen Family

• 4. ______________ - Group 17 contains flourine, chlorine, bromine, iodine, and astatine (not a non-metal). _______ means “salt forming”. Halogen atoms usually gain or share ____ electron when it reacts with other elements.

• All halogens are __________ and can be dangerous to humans.

• Many compounds that contain halogens can be useful to humans – salt, flourine in water, calcium chloride.

Halogen

The Halogen Family

one

Very reactive

Noble Gases

• __________ - elements in Group 18 that do not ordinarily form compounds because atoms of noble gases do not usually gain, lose, or share electrons.

• These gases are usually ___________.• All of the noble gases exist in the Earth’s

___________.• Noble gases were not discovered until late

1800’s because they are _______ and ________.

Noble Gases

unreactive

atmosphere

unreactive scarce

Hydrogen

• __________ - in the upper left corner of the periodic table.

• Hydrogen makes up more than ___ of the atoms in the universe.

• Hydrogen is rarely found as a ___________.

Hydrogen (H)

90%

Pure element

Metalloids

• ____________ - along the border between metals and non-metals.

• There are ___ metalloids and they have characteristics of both metals and non-metals.

• All metalloids are ____ at room temperature.• Metalloids are also brittle, hard, somewhat

reactive, varying ability to conduct heat and electricity

• ________ - most common metalloid

Metalloids

7

solid

Silicon (Si)

Semiconductors

• ____________ - substances that conduct electricity under some conditions but not under others.

• ________ are used as semiconductors because of their physical properties.

• Semiconductors are used to make _________, _____________, and ___________.

Semi-conductors

metalloids

Computer chipslasers

transmitters

Radioactive Elements

• _____________ - the atomic nuclei of unstable isotopes release fast moving particles and energy.

• _____________ - French scientist in 1896 discovered the effects of radioactive decay while he was studying a mineral that contained uranium.

• ___________ - named after __________ is the spontaneous emission of radiation by an unstable nucleus such as uranium.

Radioactive Decay

Henri Becquerel

radioactivity Marie Curie

Types of Radioactive Decay

• Natural radioactive decay can produce ___________, ____________, and ___________.

• _________ - an alpha particle consists of two protons and two neutrons and is positively charged. The release of an alpha particle by an atom is decreases the atomic number by __ and the atomic mass by __

Alpha particles Beta particlesGamma rays

Alpha decay

24

Beta Decay

• __________ - a neutron inside of the nucleus of an unstable atom changes into a negatively charged beta particle and a proton.

• __________ - fast moving electron given off by a nucleus during radioactive decay.

• Nucleus has one _____ neutron and one ____ proton – therefore, the atomic mass stays the same but the atomic number increases by __

Beta Decay

Beta particle

less more

1

Gamma Radiation

• _____________ - consists of high-energy waves – has no charge and does not cause a change in either atomic mass or atomic number.

Gamma Radiation

Effects of Nuclear Radiation

Radioactive Isotopes