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Atoms and the Periodic Table

Chapter 4

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Atomic Structure

Atoms are the simplest unit of a substance that still maintain the properties of the substance.

John Dalton proposed that atoms could not be divided.

Dalton also stated that atoms of different elements could join to form compounds.

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Parts of an Atom

Atoms are composed of subatomic particles.

Protons and neutrons are found in the nucleus of the atom.

Electrons are found in orbitals around the nucleus of the atom.

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Protons

Protons have a positive charge.

Protons have the mass of one amu (atomic mass unit).

The number of protons in an atom is characteristic of that element.

Each element has different number of protons.

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Neutrons

Neutrons have no charge.

Neutrons have the mass of one amu.

Neutrons add to the mass of an atom.

Atoms of the same element with different number of neutrons have different masses (isotopes).

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Electrons

Electrons have a negative charge.

Electrons have the mass of 1/2000 the mass of a proton.

The mass of an electron is insignificant.

The outer most electrons determine how elements combined in chemical compounds.

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Quarks A quark (IPA: /kwɔrk/) is a generic

type of physical particle that forms one of the two basic constituents of matter, the other being the

lepton. Various species of quarks

combine in specific ways to form protons and neutrons, in each case taking exactly three quarks to make the composite particle in question.

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Models of Atoms

Niels Bohr suggested that electrons in an atom move in set paths around the nucleus.

Electrons can only be in certain energy levels.

Number of electrons=2n2

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Electron Cloud Model

This model suggest that electrons orbit the nucleus in a cloud.

The regions in an atom where electrons are likely to be found are called orbitals.

The four different kinds of orbitals are the s, p, d and f orbitals.

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Valence Electrons

An electron in the outermost energy level of an atom is called a valence electron.

Valence electrons determine an atom’s chemical properties and its ability to form bonds.

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Periodic Table

The Periodic Law states that when elements are arranged this way, similarities in their properties will occur in a regular pattern.

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Structure of the Periodic Table

Horizontal rows in the periodic table are called periods.

Atoms of elements in the same group, or column, have the same number of valence electrons, so these elements have similar properties.

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Ions Formation

Atoms that gain or lose electrons form ions.

Elements that lose electrons have a positive charge (cation).

Elements that gain electrons have a negative charge (anion).

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Periodic Information

The atomic number is the number of protons in an element.

The mass number of an atom equals the number of protons plus the number of neutrons.

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Isotopes

Isotopes are atoms of the same element that have different number of neutrons.

Isotopes of the same element have different atomic masses.

The three isotopes of hydrogen are protium, deuterium & tritium.

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Mass of Atoms

An atomic mass unit (amu) is equal to one-twelfth of the mass of a carbon 12 atom.

The average atomic mass for an element is a weighted average, so the more commonly found isotopes have a greater effect on the average than rare isotopes.

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Squares on the Periodic Table

The chemical symbol is abbreviation of the chemical name. The first letter of the

chemical symbol is capitalized.

If there is more than one letter, the other letters are lower case.

Atomic number. Average atomic mass.

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Classifications of Elements

Metals are on the left side of the periodic table.

Nonmetals are on the right side of the periodic table.

Metalloids are located between the metals and nonmetals.

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Alkali Metals

This is the most reactive group of metals.

Has only 1 valence electrons.

Reacts violently with water.

Elements include Li, Na, K, Rb, Cs & Fr.

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Alkaline Earth Metals

Not as reactive as Alkali Metals.

Has two valence electrons.

Members include Be, Mg, Ca, Sr, Ba & Ra.

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Transition Metals

Members have a wide variety of properties.

Has 1, 2 or 3 valence electrons.

Contain the coin metals: gold, silver & copper.

Contain the iron triad of Fe, Co & Ni.

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Halogens

The most reactive group of nonmetals.

Has 7 valence electrons.

All members are poisonous.

Members include F, Cl, Br, I & At.

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Noble Gases

Members contain a stable octet with 8 valence electrons.

These elements do not react with other elements. Don’t form compounds.

Members include He, Ne, Ar, Kr, Xe & Rn.

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Semiconductors

Have the properties of both metals & nonmetals.

Used in the electronic industry.

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Using Moles to Count Atoms

A mole is a collection of a very large number of particles.

Avagadro’s constant is the number of particles in a mole of a pure substance.

Avagadro’s constant is 6.022 x 1023/mol.

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Molar Mass

Molar mass is the mass in grams of 1 mol of a substance.

The molar mass of an element in grams is the same as its average atomic mass in amu on the periodic table.

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Converting Moles to Grams Amount(mol) x molar mass of element/1 mol of element = mass(g)

Amount(mol)=1 mole of element/molar mass of element x mass(g)

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Converting Amount to Mass

Determine the mass in grams of 5.50 mol of iron.

Given: amount of iron=5.50 mol mol Fe molar mass of iron=55.85 g/mol Fe

Unknown: mass of iron=?g Fe 55.85 g Fe/1 mol Fe 5.50 mol Fe x 55.85 g Fe/1 mol Fe=307 g Fe

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Converting Mass to Amount

Determine the amount of iron present in 352 g of iron.

Given: mass of iron=352 g Fe

molar mass of iron=55.85 g/mol Fe Unknown: amount of iron=? mol Fe 1 mol Fe/55.85 g Fe 352 g Fe x 1 mol Fe/55.85 g Fe=6.30 mol Fe

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Sample Problem 1

A chemical reaction requires 5.00 mol of sulfur as a reactant. What is the mass of this sulfur in grams?

160.4 g S

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Sample Problem 2

For an experiment you have been asked to do, you need 1.5 g of iron. How many moles of iron do you need?

0.027 mol Fe

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Sample Problem 3

James is holding a balloon that contains 0.54 g of helium gas. What amount of helium is this?

0.14 mol He

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Sample Problem 4

A pure gold bar is made of 19.55 mol of gold. What is the mass of the bar in grams?

3851 g Au

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Sample Problem 5

Robyn recycled 15.1 mol of aluminum last month. What mass of aluminum in grams did she recycle?

407 g Al