Chem Up Fall 2017 - Daytona State College · Some Powers of Ten. Standard Format Scientific Notation Diameter of the Earth 12 800 000 m 1.28 ×107m ... Unit Conversion Using Equivalencies

F A L L 2 0 1 7

CHEM-UP!

Welcome!

• How does learning work• Scientific Notation• Significant Figures• Metric System & Conversions• Atoms, Isotopes, and Ions• Bonding• Chemical Reactions

Agenda

How Does Learning Work?We Learn

10% of what we hear

15% of what we read

20% of what we see and hear

40% of what we discuss

80% of what we experience and practice

90% of what we attempt to teach

What does this mean for you?

How can you use this to help direct your study?

Information fromhttp://www.jccmi.edu/academics/science/How_To_Study_Science/

© 2014 Pearson Education, Inc.

Scientific Notation

Scientific notation is used to write very large or very small numbers such as

• the width of a human hair, 0.000 008 m, which is also written as 8 × 10−6 m

• the number of hairs on a human scalp,100 000, which is also written as 1 × 105 hairs

• A number written in scientific notation contains a coefficient and a power of ten.

coefficient power unitof ten

1.5 × 102 m

• The coefficient is at least 1 but less than 10.


Writing Numbers in Scientific Notation

• The number of spaces moved to obtain a coefficient between 1 and 10 is shown as a power of ten.

52 000. = 5.2 × 104

move decimal 4 spaces left

0.003 78 = 3.78 × 10−3

move decimal 3 spaces right© 2014 Pearson Education, Inc.

Writing Numbers in Scientific Notation


Some Powers of Ten

Standard Format Scientific Notation Diameter of the Earth12 800 000 m 1.28 × 107 m

Mass of a human68 kg 6.8 × 101 kg

Diameter of a virus0.000 000 3 cm 3 × 10−7 cm


Comparing Numbers in Standard and Scientific Notation


Guide to Writing a Number in Scientific Notation

A measuring tool • is used to determine a quantity such as the length

or the mass of an object• provides numbers for a measurement called

measured numbers

MEASURED NUMBERS

To report the length of an object• observe the numerical values of the marked lines at

the end of the object• estimate the last digit by visually dividing the space

between the smallest marked lines

This estimated number is the final digit that is reported for a measured number.

REPORTING LENGTH

• The end of the object is between the 4-cm and 5-cm marks.

• Estimate that the end is halfway between the 4-cm and 5-cm marks and report the value as 4.5 cm.

REPORTING LENGTH – 4.5 CM

• The metric ruler is marked at every 0.1 cm.• You can now estimate that the length is halfway

between the 4.5-cm and 4.6-cm marks and report the value as 4.55 cm.

REPORTING LENGTH – 4.55 CM

Exact numbers are

• those numbers obtained by counting items

• definitions that compare two units in the same measuring system

EXACT NUMBERS

Exact numbers are not measured, do not have a limited number of significant figures, and do not affect the number of significant figures in a calculation.

EXACT NUMBERS

SIGNIFICANT FIGURES

Scientist use significant figures to determine how precise a measurement is.

Significant digits in a measurement include all of the known digits plus one estimated digit.

LET’S TRY THIS ONE

Look at the ruler below:

• What can you read before you estimate?• 12.8 cm• Now estimate the next digit…• 12.85 cm

THE SAME RULES APPLY WITH ALL INSTRUMENTS

• The same rules apply• Read to the last digit that you know• Estimate the final digit

LET’S TRY GRADUATED CYLINDERS

Look at the graduated cylinder below:

• What can you read with confidence?• 56 ml• Now estimate the last digit• 56.0 ml

ONE MORE GRADUATED CYLINDER

Look at the cylinder below…

• What is the measurement?• 53.5 ml

RULES FOR SIGNIFICANT FIGURESRULE #1

• All non zero digits are ALWAYS significant

• How many significant digits are in the following numbers?

274

25.632

8.987

3 Significant Figures

5 Significant Digits


RULE #2

• All zeros between significant digits are ALWAYSsignificant


504

60002

9.077




RULE #3

• All FINAL zeros to the right of the decimal AREsignificant


32.0

19.000

105.0020




RULE #4

• All zeros that act as place holders are NOTsignificant

• Another way to say this is: zeros are only significant if they are between significant digits OR are the very final thing at the end of a decimal

FOR EXAMPLE

0.00026.02 x 1023

100.000150000800

1 Significant Digit3 Significant Digits6 Significant Digits2 Significant Digits1 Significant Digit

How many significant digits are in the following numbers?

RULE #5

• All counting numbers and constants have an infinite number of significant digits

• For example:

1 hour = 60 minutes12 inches = 1 foot24 hours = 1 day

HOW MANY SIGNIFICANT DIGITS ARE IN THE FOLLOWING NUMBERS?

0.0073100.02025007.90 x 10-3

670.00.0000118.84

2 Significant Digits6 Significant Digits2 Significant Digits3 Significant Digits4 Significant Digits1 Significant Digit4 Significant Digits

LET’S TRY THESE EXAMPLES…

200.99 (want 3 SF)

18.22 (want 2 SF)

135.50 (want 3 SF)

0.00299 (want 1 SF)

98.59 (want 2 SF)

201

18

136

0.003

99

RULES FOR SIGNIFICANT FIGURES

SIGNIF ICANT F IGURES

CALCULATIONS

SIGNIFICANT FIGURES IN CALCULATIONS

Learning Goal Adjust calculated answers to give the correct number of significant figures.

In calculations

• calculated answers are usually rounded off• rounding rules are used to obtain the correct number

of significant figures

1. If the first digit to be dropped is 4 or less, then it and all following digits are simply dropped from the number.

2. If the first digit to be dropped is 5 or greater, then the last retained digit is increased by 1.

ROUNDING OFF

Adjust the following calculated answers to give answers with three significant figures:

A. 824.75 cm

B. 0.112486 g

C. 8.2 L

LEARNING CHECK

Adjust the following calculated answers to give answers with three significant figures:

A. 824.75 cm 825 cm

B. 0.112486 g 0.112 g

C. 8.2 L 8.20 L

SOLUTION

In addition or subtraction, the final answer is written so that it has the same number of decimal places as the measurement having the fewest decimal places.

Thousandths placeTenths placeCalculator displayAnswer, rounded off to tenths place

ADDITION AND SUBTRACTION WITH MEASURED NUMBERS

For example, 2.367

+ 34.136.46736.5

For each calculation, round the answer to give the correct number of digits.

1. 235.05 + 19.6 + 2 = (a) 257 (b) 256.7 (c) 256.65

2. 58.925 – 18.2 =(a) 40.725 (b) 40.73 (c) 40.7

LEARNING CHECK

1. 235.05 Hundredths place+19.6 Tenths place+ 2 Ones place

256.65 rounds to 257 answer (a)

2. 58.925 Thousandths place–18.2 Tenths place

40.725 rounds to 40.7 answer (c)

SOLUTION

In multiplication and division, the final answer is written to have the same number of significant figures (SFs) as the measurement with the fewest SFs.

For example,

24.65 × 0.67 = 16.5155 17

4 SF 2 SF Calculator Final answer (2 SF)

MULTIPLICATION AND DIVISION WITH MEASURED NUMBERS

ADDING SIGNIFICANT ZEROS

LEARNING CHECK

SOLUTION

Units of Measurement and Their Abbreviations

Metric Prefixes

Writing Equivalencies

Unit Conversion Using EquivalenciesAn international group of zookeepers with successful breeding programs made the following animal exchanges last year. Using the same bartering system, how many oryxes can a zoo obtain in exchange for 15 flamingos?

Step 1 Given 15 flamingos Need oryxes

Step 2 Plan flamingos anteaters camels lemurs rhinos oryxes

Step 3 Conversion Factors

15flamingos 1anteater2flamingos

1camel6anteaters

3lemurs1camel

1rhino5lemurs

=

3 oryxes

Example Problems

How many minutes are in 2.5 h?

A bucket contains 4.65 L water. How many gallons of water is that?

For more information on Unit Conversions http://oakroadsystems.com/math/convert.htm

What is an Atom? All matter is composed of atoms. They are

the building blocks of everything around us.

An atom is the smallest particle of an element that retains the element’s properties.

All atoms of a given element identical properties to one another and different properties from atoms of other elements.

Atoms combine to make molecules.

Structure of an Atom

Atoms are composed of subatomic particles called protons, neutrons, and electrons.

Protons are positively charged, electrons are negatively charged, and neutrons have zero charge.

Atoms are electrically neutral. There are an equal number

of protons and electrons in an atom.

Structure of an Atom

In an atom, the protons and neutrons make up almost all the mass of the atom. They are packed into the tiny volume of the nucleus.

The rapidly moving electrons surround the nucleus and account for the large volume of the atom. The outermost electrons are called valence electrons.

Mass of an Atom The protons and neutrons located in the nucleus

account for most of the mass of the atom. The mass of electrons are much smaller and is

often considered negligible. The mass of an atom is measured using a unit

called atomic mass unit (amu). 1 amu = 1.6605 x 10-27 kg

Atomic Number

Is specific for each element and the same for all atoms of that element.

Is equal to the number of protons in an atom.

Appears above the symbol of an element on the periodic table.

Mass Number and Atomic SymbolsMass Number Represents the number of particles in the nucleus.

Mass Number = number of protons + number of neutrons

Does not appear on the periodic table because it applies to a single atom only.

Atomic (Nuclear) Symbols Represents a particular isotope of an element.

Gives the mass number in the upper left corner and the atomic number in the lower left corner.

Mass Number

Atomic Number

Isotopes• are atoms of the same element that have different

mass numbers

• have the same number of protons, but different numbers of neutrons

• most elements have two or more isotopes that contribute to the atomic mass of that element.

ISOTOPES

VALENCE ELECTRONSElectrons orbit the nucleus in various energy

levels or shells.

Electrons in the outermost energy shell are called valence electrons.

• All elements in the same group have the same number of valence electrons.

• An elements valence electrons determines the chemical properties

• Atoms transfer or share valence electrons in order to obtain a stable electron configuration. Typically, eight or zero valence electrons.

IonsIons, which have electrical charges, form when atoms lose or gain electrons to form a stable electron configuration.

• Metals lose valence electron to form ions with positive charge.

• Non-metals gain valence electrons to form ions with negative charge.

The Octet Rule The octet rule states that elements gain or

lose electron(s) in an attempt to reach eight electrons in their outermost electron shell.

Exceptions to the octet rule include:

Hydrogen (H) and Helium (He) only attempt to gain two electrons.

Boron (B) is only capable of getting to six electrons.

Other common exceptions, include, P, S, Cl, Br, and I which can have expanded octets of 10, 12, or even 14 electrons.

Positive Ions: Loss of ElectronsA sodium atom (Na) will lose its valence electron to form a sodium ion (Na+).

Positively charged ions of metals are called cations.

Positive Ions: Loss of Electrons

Magnesium, a metal in Group 2A (2), obtainsa stable electron configuration by losing twovalence electrons, forming an ion with a2+ charge.

Negative Ions: Gain of Electrons

An atom of chlorine with seven valence electrons gains one electron to form an octet. Because it now has 18 electrons and not17 electrons, it becomes a chloride ion (Cl−)with a charge of 1−.

Negatively charged ions of nonmetals are called anions.

Transfer of Electrons

The metal transfers its valence electron(s) to the non-metal.

Ionic and Molecular Compounds Ionic bonds occur

between a metal and a nonmetal.

The nonmetal takes the electron(s) from the metal.

Covalent bonds occur between two nonmetals.

The electrons are shared.

Multiple Covalent BondsMultiple bonds form when there are not enough valence electrons to complete octets.

In a single bond, one pair of electrons is shared.

The covalent bond on the previous slide is an example of a single bond.

In a double bond, two pairs of electrons are shared.

In a triple bond, three pairs of electrons are shared.

Electronegativity is the relative

ability of atoms to attract shared electrons

is higher for nonmetals; fluorine (F) has the highest value of 4.0

is lower for metals; cesium (Cs) and francium (Fr) have the lowest value of 0.7


Dipoles and Bond Polarity

• Bonds become more polar as the difference in electronegativity increases.

• A polar covalent bond that has a separation of charges is called a dipole.

• The positive and negative ends are represented by the Greek letter delta, with a + or − charge.

• Arrows can also be used to represent dipoles.

Non-polar and Polar Covalent Bonds

Polar Covalent Bond (Dipole) Consists of an unequal

sharing of electrons between two nonmetals

Has an electronegativity difference of 0.5 to 1.7

Bonds become more polar as the difference in electronegativity increases

Non-polar Covalent Bond Consists of an equal

(or almost equal) sharing of electrons between two nonmetals.

Has a zero (or almost zero) electronegativity difference (difference of less than 0.4).

Polar and Non-polar Covalent Bonds

Chemical Reactions involve chemical change

represent the formation of a new substance with new properties

Evidence of a chemical reaction includes:

1. Formation of gas (bubbles)

2. Change in color

3. Formation of a solid (precipitate)

4. Heat is produced or absorbed

Chemical EquationsA chemical equation tells us the materials needed and the products formed in a chemical reaction.

Reactants are the materials needed.

Products are the materials built.

Some reactions are reversible.

Balanced Chemical Equations Every chemical reaction is written as a balanced

equation, such that atoms of each element are the same in the reactants and products.

To balance a reaction, coefficients are written in front of chemical formulas.

2H2(g) + O2(g) 2H2O(g)

This is due to the law of conservation of mass.

Chemical Reactions and Energy Energy must be added to break the bonds that

hold molecules together. When chemical bonds are formed in creating a product, energy is released.

The energy required to start the reaction is called energy of activation.

If the amount of energy needed to break bonds is more than the energy released when new bonds form, energy must be absorbed from the surroundings. This is called an ENDOTHERMICreaction and results in a decrease in temperature.

If the amount of energy needed to break bonds is less than the energy released when new bonds form, energy is released to the surroundings. This is called an EXOTHERMIC reaction and results in a increase in temperature.

Catalysts and Enzymes A catalyst is a substance that alters the

reaction rate of a particular chemical reaction.

Catalysts are chemically unchanged at the end of the reaction.

Catalysts can either increase or decrease the rate of a reaction by providing an alternative pathway with higher or lower activation energy.

Enzymes are a type of catalyst for biological systems. – All cells require chemical reactions to function.

Types of ReactionsCombination Reactions Two or more substances combine to form one product.

Decomposition Reactions One reactant splits into two or more simpler substances.

Types of ReactionsSingle-replacement Reaction An uncombined element replaces an element in a

compound.

Double-replacement Reactions Two elements in the reactants exchange places.

Types of ReactionsCombustion Reactions Carbon containing compounds or H2 (fuels) burn in oxygen

from the air to produce carbon dioxide CO2, water H2O. Combustion reactions are exothermic.

Examples of Combustion Reactions

Hydrogen Fire Bomb

2H2(g) + O2(g) → 2H2O(g)

The “whoosher bottle”

Alcohol (g) + O2 (g) → CO2 (g) + H2O (g)

Compiled by A. Kandefer & D. Leonard (Learning Specialists)The Academic Support Center @ Daytona State Collegehttp://www.daytonastate.edu/asc/ascsciencehandouts.html

Questions?

Documents

Chem Up Fall 2017 - Daytona State College · Some Powers of Ten. Standard Format Scientific Notation Diameter of the Earth 12 800 000 m 1.28 ×107m ... Unit Conversion Using Equivalencies