chapter 4 “chemical foundations”. section 4.1 objective: to learn about relative abundance of...

Chapter 4“Chemical Foundations”

Section 4.1Objective: to learn about relative abundance of the elements and learn some names of elements

The ElementsElement Name Relative Abundance

• Oxygen• Silicon• Aluminum• Iron• Calcium• Sodium• Potassium• Magnesium• hydrogen

• 49.2%• 25.7%• 7.5%• 4.71%• 3.39%• 2.63%• 2.4%• 1.93%• 0.87%

How the Term Element is Used

• Could mean a single atom of that element ▫ (Ar or H).

• Could mean molecules of an element▫ (H2, N2, O2, F2, Cl2, Br2, I2), which are

found in their natural states.• Could mean atoms of elements are

present in some form ▫ (sodium found in the human body).

• Look at each particular case to determine its proper use.

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Section 4.2Objective: to learn the symbols for the elements

• 115 known: 88 found in nature, others are man made.

• Just as you had to learn the 26 letters of the alphabet before you learned to read and write, you need to learn the names and symbols of the chemical elements before you can read and write chemistry.

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Names & Symbols

•One or two letter ▫Fluorine F Neon Ne

•First letter is CAPATALIZED, the second is not▫Silicon Si Argon Ar

•Not always first two letters of element▫Zinc Zn Chlorine Cl

•Sometimes based on other languages▫ gold (aurum) Au Iron (ferrum) Fe

Law of Constant Composition• A given compound always has the same

composition, regardless of where it comes from. Water always contains 8 g of oxygen for

every 1 g of hydrogen. Carbon dioxide always contains 2.7 g of

oxygen for every 1 g of carbon.

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Section 4.4objective: to learn how a formula describes a compound's composition

Chemical Formulas Describe Compounds

• Compound – distinct substance that is composed of the atoms of two or more elements and always contains exactly the same relative masses of those elements.

• Chemical Formulas – expresses the types of atoms and the number of each type in each unit (molecule) of a given compound.

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Rules for Writing Formulas

1. Each atom present is represented by its element symbol.

2. The number of each type of atom is indicated by a subscript written to the right of the element symbol.

3. When only one atom of a given type is present, the subscript 1 is not written.

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Exercise

The pesticide known as DDT paralyzes insects by binding to their nerve cells, leading to uncontrolled firing of the nerves. Before most uses of DDT were banned in the U.S., many insects had developed a resistance to it. Write out the formula for DDT. It contains 14 carbon atoms, 9 hydrogen atoms, and 5 atoms of chlorine.

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C14H9Cl5

Section 4.9Objective: to understand diatomic molecules

Diatomic Molecules• Most elements quite

reactive▫ so they form compounds

to become more stable▫ When found alone in

nature, (not combined with other elements in compounds), these elements exist only as two covalently bonded atoms

• Some we give a special name to:▫ Diatomic molecules

Molecules made up of two atoms

Diatomic Molecules

• Nitrogen gas contains N2 molecules.

• Oxygen gas contains O2 molecules.

Copyright © Cengage Learning. All rights

reserved

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Section 4.8Objective: learn various features of the periodic table

Mendeleev’s Table

Mendeleev arranged the elements in order of increasing relative atomic mass (protons had not been discovered yet). The elements on the modern periodic table are arranged in order of increasing atomic number.

He also grouped elements with similar properties into columns and rows so that the properties of the elements varied in a regular pattern (periodically).

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2 -

Russian chemist Dmitri Mendeleev developed and published the basic arrangement of the periodic table between 1869 and 1871.

The Periodic Table:A Preview A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties

The periodic table allows you to easily compare the properties of one element to another

The Periodic Table: Row vs Group

Each horizontal row (there are 7 of them) is called a period

Each vertical column is called a group, or familyElements in a group have similar chemical and physical propertiesIdentified with a number and either an “A” or “B”

Families

Rare Earth Metals are the collective group of lanthanide and actinide series

• Most elements are very reactive.• Elements are not generally found in

uncombined form. Exceptions are:

Noble metals – gold, platinum and silver

Noble gases – Group 8

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Periodic Table

Helium Neon Argon Krypton Xenon

Metal vs Nonmetal vs Metalloid

Properties of Metals

•Efficient conductors of heat and electricity

•Malleable (hammered into thin sheets)•Ductility (pulled into thin wires)•Lustrous (shiny) appearance

Atoms

Sizing up the Atom

Elements are able to be subdivided into smaller and smaller particles – these are the atoms, and they still have properties of that element

If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm longDespite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) microscopes

The atom contains:• Electrons –

▫ found outside the nucleus

▫ negatively charged• Protons –

▫ found in the nucleus▫ positive charge equal in

magnitude to the electron’s negative charge

▫ atomic number• Neutrons –

▫ found in the nucleus

▫ no charge▫ virtually same mass as a

proton -atomic mass p+n

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• The nucleus is: Small compared with the overall size

of the atom. Extremely dense; accounts for

almost all of the atom’s mass.

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Subatomic Particles

ParticleParticle ChargeCharge Mass (g)Mass (g) LocationLocation

ElectronElectron

(e(e--)) -1-1 9.11 x 109.11 x 10-28-28 Electron Electron cloudcloud

ProtonProton (p(p++)) +1+1 1.67 x 101.67 x 10-24-24 NucleusNucleus

NeutronNeutron

(n(noo)) 00 1.67 x 101.67 x 10-24-24 NucleusNucleus

We have had many models of the atom (we will discuss this more in detail in a later chapter), but for now we will look at the Bohr Model and Lewis Dot Structures

Neil Bohr’s Atomic Modelelectrons orbit nucleus like planets around sun

Example 1 (3D model) “Jimmy Neutron” Example 2 (2D model)

Atomic Number•Atoms are composed of identical

protons, neutrons, and electrons▫How then are atoms of one element

different from another element?•Elements are different because they

contain different numbers of PROTONS•The “atomic number” of an element is

the number of protons in the nucleus

Atomic Number

Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

ElementElement # of protons# of protons Atomic # (Z)Atomic # (Z)

CarbonCarbon 66 66

PhosphorusPhosphorus 1515 1515

GoldGold 7979 7979

Question: How do I know how many electrons each element has?

4 Be Beryllium

9.012

•On the periodic table the ATOMIC NUMBER also tells you how many electrons there are

•Because:▫ #of protons = #

of electrons

Atoms have an overall neutral charge

• # of p+ = # of e- ▫number of protons equals the number of

electrons• example….helium has atomic number of 2

▫Protons = +2▫Neutrons = 0▫Electrons= -2

---------------------• Total charge 0

Remember this is ONLY true on the periodic table. It is not true in “real life”

Why do different atoms have different chemical properties?

• The chemistry of an atom arises from its electrons.

• Electrons are the parts of atoms that “intermingle” when atoms combine to form molecules.

• It is the number of electrons that really determines chemical behavior.

• Specifically VALENCE ELECTRONS

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Valence Electrons•Electrons found in the outermost energy

level of an atom.▫Determine:

1. Chemical properties 2. Atoms ability to form bonds

•Every atom has between 1 and 8 valence electrons

•Group number helps to determine valence electrons Stop Bohr model

Lewis Dot Structures• What are the valence electrons?

▫They determine a elements unique properties▫They are also the electrons that are used in

bonding• Only these outer electrons want to bond? Why?

▫all other electrons (in their energy levels) are happy

▫ therefore scientists want to focus their attention on these specific electrons

• Lewis dot structures ▫ Show only the valence electrons

• How do we figure out the number of valence electrons?▫ GROUP NUMBER

So where are the electrons?•If Bohr model isn’t accurate and Lewis’s

just shows us valence electrons where are the electrons exactly?

•MODERN ATMOIC THEORY▫Electrons are found in orbitals/clouds

(regions around the nucleus where the electrons are likely to be found)

▫best scientists can do is calculate chance of finding electron in certain place within an atom

▫Electron move very fast.

Modern Atomic Theory

Figuring out the number of protons, electrons, neutrons

• Determining subatomic particles in elements (GENERIC)• Element symbol (X)one/two/three letter symbol for element • Atomic number (Z) number of protons found in the element• Mass number (A)number of protons + the number of

neutrons• The periodic table will give you all the information you need

in order to calculate protons, neutrons and electrons

X Massnumber

Atomicnumber

Subscript →

Superscript →

4 Be Beryllium 9.012

Atomic Number = Number of protons and number of electrons. On the periodic table all elements are neutral. Therefore p = e

Average Atomic Mass Number = Number of protons and number of neutrons. Sometimes p = nSometimes p = n

Element Symbol = symbol for element: usually first letter or two letters of its name. However, not in all cases. WHY?

Element Name = Full name of the element

Mass NumberMass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0

NuclideNuclide pp++ nn00 ee-- Mass #Mass #

Oxygen - - 10

- - 33 42

-- 31 15

8 8 1818

Arsenic 75 33 75

Phosphorus 15 3116

SymbolsSymbols Find each of these: Find each of these:

a)a) number of protonsnumber of protons

b)b) number of number of neutronsneutrons

c)c) number of number of electronselectrons

d)d) Atomic numberAtomic number

e)e) Mass NumberMass Number

Br80 35

SymbolsSymbols If an element has an atomic If an element has an atomic

number of 34 and a mass number of 34 and a mass number of 78, what is the: number of 78, what is the:

a)a) number of protonsnumber of protons

b)b) number of neutronsnumber of neutrons

c)c) number of electronsnumber of electrons

d)d) complete symbolcomplete symbol

SymbolsSymbols If an element has 91 If an element has 91

protons and 140 neutrons protons and 140 neutrons what is the what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of electronsnumber of electrons

d)d) complete symbolcomplete symbol

SymbolsSymbols If an element has 78 If an element has 78

electrons and 117 neutrons electrons and 117 neutrons what is the what is the

a)a) Atomic numberAtomic number

b)b) Mass numberMass number

c)c) number of protonsnumber of protons

d)d) complete symbolcomplete symbol

Isotopes

Isotopes

•Atoms of the same element can have different numbers of neutrons.

•Thus, different mass numbers.•These are called isotopes.

Isotopes

•Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912

• Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. (same P, different N)

•Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.

Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

IsotopeIsotope ProtonsProtons ElectronsElectrons NeutronsNeutrons NucleusNucleus

Hydrogen–1Hydrogen–1

(protium)(protium) 11 11 00

Hydrogen-2Hydrogen-2

(deuterium)(deuterium) 11 11 11

Hydrogen-3Hydrogen-3

(tritium)(tritium)

11 11 22

Naming Isotopes

•We put the mass number after the name of the element:▫carbon-12▫carbon-14▫uranium-235

Isotopes• Isotopes- an element with the different

numbers of neutrons▫Most element have a number of different isotopes

For example C-12, C-13, and C-14.• We use C-14 to carbon date fossils

▫Scientists take an average of these atomic masses▫ In this calculation the abundance of the isotope is

also calculated For example the atomic mass of C is 12.01

• Can you hypothesize which C isotope is most abundant▫ ***therefore rare isotopes have little effect on the

atomic mass

Atomic Masses

IsotopeIsotope SymbolSymbol Composition of Composition of the nucleusthe nucleus

% in nature% in nature

Carbon-12Carbon-12 1212CC 6 protons6 protons

6 neutrons6 neutrons

98.89%98.89%

Carbon-13Carbon-13 1313CC 6 protons6 protons

7 neutrons7 neutrons

1.11%1.11%

Carbon-14Carbon-14 1414CC 6 protons6 protons

8 neutrons8 neutrons

<0.01%<0.01%

Atomic mass is the average of all the naturally occurring isotopes of that element.

Carbon = 12.011

IsotopesElements occur in nature as mixtures of isotopes.

Remember: Isotopes are atoms of the same element that differ in the number of neutrons.

Exercise

A certain isotope X contains 23 protons and 28 neutrons.

•What is the mass number of this isotope?•Identify the element.

Mass Number = 51Vanadium

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Remember an element is determined by the number of protons it has*

• What happens if you change the number of protons of an element?▫ You have a completely different element

• What happens if you change the number of neutrons?▫ you still have same element but this element has a

different number of neutrons then the original element……. This is an isotope

• What happens if you change the number of electrons?▫ You have the same element….but the element has a

charge (either positive or negative) This is called an ION

Ions

Ions

•Are atoms of an element with an unequal number of protons and electrons

•Everything is based off the electron•ion charge also called Oxidation Number•Represented as Mg+2 or OH -1

▫Cation = + ion (loses an electron, therefore has more protons (+) then electrons)

▫Anion = - ion (gains an electron, there has more electrons (-) then protons)

• Atoms can form ions by gaining or losing electrons. Metals tend to lose one or more electrons

to form positive ions called cations.

Cations are generally named by using the name of the parent atom.

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Ions

• Nonmetals tend to gain one or more electrons to form negative ions called anions.

• Anions are named by using the root of the atom name followed by the suffix –ide.

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Ions

Oxidation Number*remember atoms want to be stable*everyone wants to be like the last column (noble gases) and have ______ valence electrons. Exceptions?

• How do atoms do this?▫Atoms want to get to that stable outer valence

shell of 8 electrons.• Oxygen has ______ valence electrons;

therefore it needs _____ more to get to eight. • IF AN ATOM NEEDS TO GAIN ELECTRONS

THE OXIDATION NMUMBER IS NEGATIVE. THE ATOM IS IN NEED. LIKE A DEBT……THE ATOM NEEDS MORE MONEY (electrons)

• If an atom needs 2 more electrons; its If an atom needs 2 more electrons; its oxidation number is -2 (negative 2)oxidation number is -2 (negative 2)

•Fluorine has _________ valence electrons; therefore it needs ________ more to get to eight.

•If an atom needs 1 more electron; its oxidation number is -1 (negative 1)• Nitrogen has ________ valence electrons: therefore it needs _____ more to get to eight

•If an atom needs 3 more electrons; its oxidation number is -3 (negative 3)

•NEXTLithium has _____ valence electrons: how

does it get to be stable?

What is easier to gain 7 electrons or get rid of one?IF AN ATOM HAS EXTRA ELECTRONS THE OXIDATION NUMBER IS POSITIVE. THE ATOM HAS MORE THEN IT NEEDS. LIKE A CREDIT……YOU HAVE EXTRA MONEY (ELECTRONS)TO LOAN Lithium has ________ valence electrons: therefore it can loan ______ more to become stable

What is easier to gain 7 electrons or get rid of one?IF AN ATOM HAS EXTRA ELECTRONS THE OXIDATION NUMBER IS POSITIVE. THE ATOM HAS MORE THEN IT NEEDS. LIKE A CREDIT……YOU HAVE EXTRA MONEY (ELECTRONS)TO LOAN Lithium has ________ valence electrons: therefore it can loan ______ more to become stable

If an atom can loan 1 electrons; its oxidation number is +1 (positive 1)

There is a trend in the oxidation number on the periodic chart. Can you find it?

• Beryllium has ___________ valence electrons; therefore it can loan ________more to become stable.

• I f an atom can loan 2 electrons; its oxidation number is +2 (positive 2)

• Carbon has __________ valence electrons; it is right in the middle; therefore it can gain or loan 4 electrons

• 1... if an atom can gain OR loan 4 electrons; its oxidation number is +/- 4 (positive or negative 4)

Oxidation trend in the periodic table

Section 4.11Objective: learn how ions combine to form neutral compounds

• Ions combine to form ionic compounds.

• Properties of ionic compounds High melting points Conduct electricity

If melted If dissolved in water

• Ionic compounds are electrically neutral.

• The charges on the anions and cations in the compound must sum to zero.

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Compounds that Contain Ions

Formulas for Ionic Compounds

• Write the cation element symbol followed by the anion element symbol.

• The number of cations and anions must be correct for their charges to sum to zero.

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This chapter will be referred to on a daily basis from here on out. If you do not know and understand this chapter

YOU WILL BE LOST!