Chapter 17 chemistry grades 5-8

Structure of Matter

Chapter 17

17-1 Atoms, Elements, and Molecules

ObjectivesO Describe the structure of matterO Describe the relationship between

atoms, elements, and moleculesO Identify the symbols of common

elements

Alphabet

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The English alphabet has 26 letter, elements. By using these letters in the right

order, you can write any of multitude of words, which, in turn, can be combined into sentences and paragraphs

Matter

Matter is organized in a similar way. There are over

100 different elements. When these 100 elements are arranged in the proper order, they form familiar compounds, substances

and structures.

VocabularyO Element – made up of all the same

kinds of atoms, each with the same number of protons and electrons.

O Symbol – one of two letters that represent the name of the element.

O Molecules – any combination of two of more atoms that are chemically combined.

ElementsO An element cannot be broken down

into simpler substances and still retain all of its physical properties.O For example the number 1108 stops

being 1108 when you erase any of the four digits.

MoleculesO Molecules are combination of atoms

that are chemically changed. O They may be the same element or the

atoms that combine to form molecules may be of different elements

O May be 2 atoms or 50, 100, or even 1000 atoms.

17-2 Atomic ParticlesO Objectives:

O Identify the atomic particlesO Distinguish between the planetary

and the electron-cloud models of the atom.

Parts of the atomsO Three basic parts:

O The protonO The electronO The neutron

Proton

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The proton is a very small particle that has a positive

(+) charge.

Electron

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The electron is smaller still and has a negative (-)

charge.

Neutrons

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The neutron is about the same size and mass as the proton, but has no charge.

(0)

VocabularyO Electron probability cloud – uses

regions instead of fixed orbits of the planetary model.

O Energy level – the amount of energy of an electron

O Quantum – the amount of energy an atom gains or loses

O Quark – a tiny particle that makes up protons and neutrons.

Planetary ModelO Neils Bohr pictured the atoms like a

tiny solar system.

O The protons and neutrons of helium are packed tightly together in the center of the atom.

Planetary ModelO According to this model, an electron can

orbit the nucleus only at certain distances from the nucleolus.

O In any given orbit, or energy level, an electron has a definite amount of energy.

O When an atom gains energy, one of the its electrons moves to an orbit with a larger radius.

O An atom releases energy when one of its electrons moves to a smaller orbit.

Atomic ParticlesO The amount of energy gained or released equals the

energy difference between the two orbits. O Scientists say that energy in the atom exist as units,

because it can gain or lose only definite amounts of energy, or quantum.

O The planetary model of the atom served a purpose but is now longer adequate because scientists discovered that electrons did not stay in fixed orbits.

O The electron-cloud model uses electron probability clouds or regions instead of fixed orbits of the old planetary model.

O The probability model also predicts which energy changes are more likely to occur and which ones are less likely.

AtomsO Quantum ideas are now common in

our everyday languageO Small change in energy a “quantum

step”O Large change in energy a “quantum

leap”

17-3 Atomic Number and Atomic Mass

O Objectives Distinguish between atomic mass and atomic numberExplain how atoms of the same element can differDescribe how scientists identify isotopes.

Atomic number

Gold Nugget79 protons

Mercury80 protons

O Solid O Liquid

Atomic NumberO It seems amazing that just the addition

or deletion of a proton can result in such a major difference.

O The atoms of each element have a specific number of protons: this number is the atomic number.

O The number of protons equals the number of electrons

O This pattern continues until number 109 on the periodic table.

Atomic MassO Atomic mass equals the number of

protons and neutrons in an atom. O Atoms of the same element always have

the same number of protons.O Atoms of the same element that have

different numbers of neutrons are called isotopes. O Carbon 12 has 6 protons and six neutronsO Carbon 14 has 6 protons and eight

neutrons

17-4 The Periodic TableO Objectives:

O Describe the organizations of periodic table

O Identify the characteristics of metals, nonmetals, metalloids, noble gases.

The Periodic TableO Before the year 1500, scientists could identify

only 11 of the 109 elements. O The Bible mentions at least five of these when

it refers to iron, silver, gold, lead and tin. O Six more elements –carbon, sulfur, arsenic,

antimony, bismuth, and mercury – were also known.

O Through the centuries scientist added more elements to the table and today we have either 114 or 118, depending on who you talk to.

O Today, scientists are working to create new elements.

Periodic TableO During the 1800s enough elements

were known for scientists to start seeing patterns among them.

O In 1869, a Russian Chemist, Dmitri Mendeleev recorded the elements in columns, placing similar elements in a horizontal row.

O The orderliness of the known elements became more apparent.

The horizontal rows of elements are called periods. Elements in the same period have electrons in the same energy levels.Each vertical column of the periodic table is called a group.Elements in the same group have similar physical and chemical properties.

Periodic TableO There are seven periods and eighteen

groups, each labeled with a numeral.O Each element is give a block on the

periodic table, which contains the chemical symbol for the element.

O Elements that border the line between metals and nonmetals are called metalloids.

O These elements sometimes act like metals and at other times act like nonmetals.