TAKS Objective 4

Matter and Change

States of Matter

• All matter has mass and takes up space, yet matter can exist in different states.

• There are three main states of matter– 1. Solid– 2. Liquid– 3. Gas

• Every solid has a definite volume and a definite shape.

• The particles are tightly compressed.

Solids

Liquids

• A liquid flows and takes the shape of its container.

• Liquid matter has a definite volume but no definite shape.

• Gases expand or contract to fill the space available to them. They can also compress to fill smaller spaces.

• A gas has neither a definite shape or a definite volume.

Energy

Properties of Fluids

Density

• Size and shape do not change an object’s density.

• Example: a candle’s density is determined, then you melt the wax. What is the melted wax’s density? The same as the candle that was not melted.

• The density of solids usually decreases slightly as temperature increases because solids expand when heated.

• Ice is less dense than water. Because of this, the ice floats in water.

• The formula for density is: d=m/v

MRemember…

this line means to multiply

And this line means to

divide

A block of maple wood with a volume of

405 cubic centimeters and a density of

0.67 g/cm3 is sawed in half. The density

of the two smaller blocks is now —

A one-fourth the original density

B one-half the original density

C two times the original density

D the same as the original density

A sample of an element has a volume of 78.0 mL and a density of 1.85 g/mL. What is the mass in grams of the sample? Record and bubble in your answer to the nearest tenth on the answer document.

Use the formula page, D = m/v…now set up in a triangle…

1.85 78.0

and solve…1.85 X 78.0 = 144.3

Buoyancy of Fluids

Buoyancy • Buoyancy is a measure of the upward

pressure a fluid exerts on an object.

Buoyant Force

• If the buoyant force is greater than its weight, the object floats.

• If the buoyant force is less than its weight, then the object will sink.

HELP! I am drowning

because the buoyant

force is less than my body

weight!!!

Viscosity of Fluids

Viscosity

• Viscosity is the measure of a material’s resistance to flow.

• High-viscosity fluids take longer to pour from a container than low-viscosity fluids.

• Example: High-viscosity = syrup

Low-viscosity = water

Temperature Affects Viscosity

• As the temperature of a liquid is raised, the viscosity decreases.

• Example: warm hot fudge is much easier to pour than when it is cold

The Periodic Table

Atoms are. . .

• The smallest part of a single element.

• The basis of all matter. • Made of mostly empty

space. • Have a positive core or

nucleus. • Have electrons

orbiting in clouds.

Parts of an Atom

• Protons– Located inside the nucleus– Have a positive charge

• Neutrons– Located in the nucleus– Have a neutral charge or no charge

• Electrons– Orbit around the nucleus– Have a negative charge

Atomic Number

• The atomic number is the number of protons in the element’s nucleus.

• Every atom of the same element has the same atomic number.

• Ex: Every carbon atom has 6 protons

• The number of electrons in an atom equals the number of protons in that atom.

I see…the atomic number is like a person’s DNA…

it’s what identifies us.

• When the atom has equal numbers of protons and electrons it is said to be electrically neutral.

• This is because the positive charges equal the negative charges, therefore, there is no charge.

Mass Number or Atomic Mass

• The mass number is the sum of the number of protons and neutrons in the nucleus

• Number of neutrons = mass number – atomic number

Isotopes

• Atoms of the same element that have different numbers of neutrons are called isotopes

• To determine the number of neutrons in an isotope:

• Mass number – Number of protons = Number of neutrons

4 Basic Types of Elements• Metals: found to the left of the stair-step

line • Non-metals: found on the right side of

the stair-step line• Metalloids: found along the stair-step

line • Synthetic: made in the laboratory and

not yet found in nature – many of the Actinide and Lanthanide series and very large # elements.

Where are the metal elements?

Left of the Stair-step line!

Properties of Metals

• Metals are: –Conductors –Lustrous (shiny) –Electron donors –Malleable (rolled into

sheets – Aluminum foil)–Ductile (pulled into wires)

Where are the nonmetals? To the Right of the stair step line, and Hydrogen!

Properties of Nonmetals

• Nonmetals are brittle, insulators, electron acceptors

• Usually form negative ions (except H) • Many are gases at room temperature • Found to the right of the stair-step

According to the periodic table, which element most readily accepts electrons?

• A Fluorine• B Nitrogen • C Arsenic • D Aluminum

Fluorine only needs 1 electron to complete its shell of 8, so it will accept it from any other element very very very easily. This periodic property increases as you move up and left in the table, except for the Noble Gases.

Use the Table provided! What do the numbers mean?

22.990

sodium

This is the atomic number. It is the number of protons in a single atom of this element. By the way, its also # of electrons.

The symbol for this element.

This is the atomic mass, it is the number of protons + neutrons, or the mass of the nucleus of an atom.

This is the name of the element.

Transition Elements

• The transition elements are located in groups 3-12 of the periodic table.

• These elements are very hard, with high melting points and boiling points.

Alkali Metals

• The alkali metals, found in group 1 of the periodic table are very reactive metals.

• They have only one electron in their outer shell. Therefore, they are ready to lose that one electron in ionic bonding with other elements.

Alkaline Earth Metals

• The alkaline earth elements are metallic elements found in the second group of the periodic table.

• All alkaline earth elements have an oxidation number of +2, making them very reactive.

Halogens

• The halogens are five non-metallic elements found in group 17 of the periodic table.

• All halogens have 7 electrons in their outer shells, giving them an oxidation number of -1.

• The halogens exist, at room temperature, in all three states of matter:

– Solid- Iodine, Astatine – Liquid- Bromine – Gas- Fluorine, Chlorine

Noble Gases

• The noble gases are found in group 18 of the periodic table.

• All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them the most stable.

Valence Electrons

• Valence electrons are those electrons that an atom uses in forming a bond with another atom.

• These electrons are found in the outermost shell of an element.

• Look at your periodic table. You should see roman numerals with A’s beside them. These tell you the number of valence electrons.

Valence electrons• How many valence electrons does

Calcium have?

• How many valence electrons does Oxygen have?

• How many valence electrons does Chlorine have?

Important Note!!!!

• Atoms in the same group have similar chemical properties because they have the same number of valence electrons.

Which of the following groups contains members with similar chemical reactivity?

A Li, Be, C

B Be, Mg, Sr

C Sc, Y, Zr

D C, N, O

Lets look at the Table provided.• To have similar

chemical properties of any kind, they must be in the same Group or Family.

• Groups are columns, so the answer would be

A Li, Be, C

B Be, Mg, Sr

C Sc, Y, Zr

D C, N, O

Oxidation Numbers

• The oxidation number tells how many electrons an element can accept, lose, or share when bonding.

• If it has a positive oxidation number, then it tends to lose electrons.

• If it has a negative oxidation number, then it likes to gain electrons.

Look at your periodic table and label the oxidation numbers as follows:

+2 +3 +4 -3 -2 -1

These are the transition metals, and they have varying oxidation numbers!

+2 +3 +-4 -3 -2 -1

Make sure you label these on the actual TAKS test!!

Chemical Reactivity • Metals

increase in reactivity left and down.

• Nonmetals become more reactive up and to the right.

• Most reactive metal is?

• Most reactive nonmetal is?

TAK Obj. 04TEKS I.7D

Remember that # of electrons = # of

protons in a neutral atom and protons identify

the element

Ionic Compounds

Two Main Types of Bonds:

• Ionic– Forms between a positively charged ion and

a negatively charged ion– A metal and a nonmetal

• Covalent– 2 nonmetals– The electrons are shared

Ionic Compounds • Ionic bond – the force that holds

oppositely charged particles together.• Ionic compounds contain ionic bonds• Ionic compounds consist of cations

(positive ions) and anions (negative ions).

Ionic Formulas

• A formula is the symbols used to make up a compound.

• Ex: NaCl = sodium chloride• Calcium chloride’s formula is CaCl2. The

2 is a subscript, which means that it is written below.

• A subscript tells the number of atoms of the chemical written before it.

• If a subscript is not present, then the subscript is assumed to be 1.

• Example: Fe2O3

– There are two atoms of iron and three atoms of oxygen

The chemical formula for any compound tells what elements it contains and the ratio of the atoms of those elements.

Ions and Ionic Bonds

• When an element loses electrons it gets a + charge associated with it. Refer to your oxidation numbers on your periodic table!!

• Ex: Mg2+ means that magnesium now has a +2 charge or has lost 2 electrons.

• Superscript means written above. The 2+ written above Mg is the superscript.

• When a superscript is used, it tells the charge that is on that element.

• The charge on an element can be positive or negative– If you lose electrons, then the charge is

positive– If you gain electrons, then the charge is

negative

Remember!!!

• Ionic compounds are normally formed between a metal and a nonmetal.

• Covalent bonds are normally formed between nonmetals.

Rules for Writing Binary Compounds

• 1. Write the symbol of the first element which has a positive oxidation number

• 2. Write the symbol of the element which has a negative oxidation number

• 3. Add subscripts so that the sum of the oxidation numbers of all the atoms is zero

• You can use the criss-cross method as a shortcut!

Example problem

• What is the formula for a compound containing only aluminum and sulfur?

• 1. Write the symbol of the element with the positive oxidation number followed by the symbol of the element with the negative oxidation number – Al S

• Look up the oxidation numbers and write them above the symbols– 3+ 2-

Criss-Cross Shortcut

Al+3 S-2

32You still have to write down the symbols and their oxidation numbers, but now you can just criss-cross the oxidation numbers and drop their signs to get your formula!

Rules for Naming Ionic Compounds

• 1. Write the name of the first element • 2. Write the root of the second element• 3. Add –ide to the end of the second

element

• Chlorine – chlor• Fluorine – fluor• Nitrogen – nitr• Oxygen – ox• Phosphorous – phosph• Sulfur - sulf

Example problem

• What is the name of Li2S?• Write the name of the positive element

– lithium• Write the root of the second element

– sulf-• Add –ide to the end of the second

element– Answer: lithium sulfide

Water is made up of 2 Hydrogen atoms covalently bonded to an Oxygen atom.

Covalent Bond Covalent

Water is a polar molecule, which means one end has a positive charge and one end has a negative charge

H H+ +

Slighlty positive charge

Slightly negative charge

The polarity of water allows it to easily dissolve ionic compounds.

Water is the universal solvent !!!

Opposite charges attract

Elements, Compounds, & Mixtures

Matter • Anything that has mass and takes up space.–Dog, car,

computer, candy

• Energy is NOT matter

Matter is divided into 2 categories:

• Pure Substances• Mixtures

Matter Flowchart

MATTER

Can it be physically separated?

Homogeneous Mixture

(solution)

Heterogeneous Mixture Compound Element

MIXTURE PURE SUBSTANCE

yes no

Can it be chemically decomposed?

noyesIs the composition uniform?

Pure Substances

• Element– composed of identical atoms– EX: copper wire, aluminum foil

Pure Substances

• Compound

– composed of 2 or more elements in a fixed ratio

– properties differ from those of individual elements

– EX: table salt (NaCl)

Mixtures

• Variable combination of 2 or more pure substances.

Heterogeneous Homogeneous

There are two types of mixtures:

• Heterogeneous- mixture is not the same from place to place. – Chocolate chip

cookie, gravel, soil.

• Homogeneous- same composition throughout.

– Kool-aid, air, brass.

Mixtures

• Solution– homogeneous– very small particles

– particles don’t settle– EX: rubbing alcohol

Decide if the substance is Element, Compound , or Mixture?

1. Water

2. Table Salt

3. Oxygen

4. Dirt

5. Air

1. Compound

2. Compound

3. Element

4. Heterogeneous Mixture

5. Homogeneous Mixture/Solution

6. Copper

7. Soda

8. Steel

9. Acid Rain

10. Vanilla Ice-cream

6. Element

7. Solution/Homogeneous Mixture

8. Solution/Homogeneous Mixture

9. Heterogeneous Mixture

10. Homogeneous Mixture

Let’s try a few more!

Physical and Chemical Changes

Changes in Matter – Physical or Chemical?

• Physical changes are changes in the state of matter. They do not change the substance. (Melting, boiling, condensing, freezing, cutting)

• Chemical changes are reactions that result in new products with new properties.

Physical Changes

• Physical changes are about energy and states of matter.

• When you step on a can and crush it, you have forced a physical change. The shape of the object has changed. It wasn't a change in the state of matter, but something changed.

Chemical Changes

• When iron (Fe) rusts you can see it happen over a long period of time. The actual molecules have changed their structure (the iron oxidized).

Changes in Matter – Physical or Chemical?

• Physical changes • Cutting a piece of

wood does not change the wood, it is simply smaller.

• Chemical changes• When a different

substance is produced than what was present at the start, a chemical change has occurred.

Let’s try some problems…

1. Cutting your hair 1. physical

2. Fire burning 2. chemical

3. Ice melting 3. physical

4. Water evaporating 4. physical

5. Tomato rotting 5. chemical

Let’s try some more…6. Sodium combines with chlorine to produce table salt.

6. chemical7. Glass breaking 7. physical

8. Food digesting 8. chemical

9. Water is broken down into hydrogen & water

9. chemical

10. photosynthesis 10. chemical

Conservation of Mass

• The Law of Conservation of Energy says that energy can neither be created nor destroyed.

• Massreactants = Massproducts

According to the law of conservation of mass, how much zinc was present in the zinc carbonate?

A 40 g B 88 g C 104 g D 256 gSince matter can not be created or destroyed in chemical reactions, the mass on both sides of the arrow must be equal. So 64g + 192g = 256g and 152 g + Zinc = 256g

There must be 104g of Zinc. Answer C.

Balancing Chemical Equations

Chemical Reactions

• A chemical reaction is a change in which one or more substances are converted to different substances

Chemical Reactions Since matter can not be

created or destroyed, chemical reactions must be balanced in terms of mass.

The amount of mass you start with must be equal to the mass of the products.

Reactants Products

100g total = 100g total

Counting Atoms• Whole numbers written in front of formulas

are called coefficients. For example, 4 C6H12O6 indicates that there are 4 molecules of glucose sugar.

• To determine how many total atoms of each element are present, multiply the coefficients by the subscripts for each element.

• 4 C6H12O6 would contain 24 atoms of carbon (4 x 6), 48 atoms of hydrogen (4 x 12), and 24 atoms of oxygen (4 x 6).

• Reactants – the chemicals that will react– They are to the left of the arrow

• Products – the chemicals that are produced– They are located to the right of the arrow

• Reactants Products

Chemical Equation

• A chemical equation is an expression that describes a chemical reaction using chemical formulas and other symbols

• H2 + O ------ H2O

To balance equations: • The number of atoms of each type of

element on the reactant side (left of the arrow) must be equal those on the product side (right side of the arrow).

2 H2 + O2 2 H2O

• There are 4 hydrogen atoms on the left (2 H2) and 4 hydrogen atoms on the right (2 H2O)

• There are 2 atoms of oxygen (O2) on the left and 2 atoms of oxygen on the right (2 H2O). When a subscript is missing, it is understood to be 1.

• Coefficients are the numbers that are placed beside the chemical formulas to balance chemical equations

• 2H2 + 2O ------ 2H2O– The underlined numbers are the coefficients

Balanced Chemical Equations

• Has the same number of atoms of each element on both sides of the chemical equation

• You can NEVER change the subscripts in a chemical equation!

• You must instead place whole numbers in front of the chemical formulas!

• If there is no coefficient, then it is assumed to be one.

Rules for Balancing Chemical Equations

• 1 – under the reactants, list each element’s symbol

• 2 – calculate how many atoms are associated with each element

• 3 – repeat steps 1 and 2 for the products• 4 – begin adding coefficients in front of the

chemical formulas to try to get the same number of atoms on each side

• HINT: do NOT try to balance hydrogens and oxygens first! Balance all other elements first!

• 5 – double check that all elements on the reactant side match their counterpart on the product side of the equation

Example