Elements, Compounds and Mixtures

Physical Science

Elements, Compounds and Mixtures

• Element – The purest substance that cannot be separated into simpler substances by physical or chemical means.

• Ex: a 5 gram (g) nugget of gold is like every other particle of gold. This is how you can identify gold found in rock.

Periodic Table of Elements

Identifying Elements by Their Properties

• Each element has its own characteristic properties, both physical and chemical. Look at the examples on page 83.

• Elements are grouped into categories according to their shared properties. For example, metals are not all alike, but they share enough in common to be grouped into the metals category.

Identifying Groups by Their Properties

• Metals – shiny, good conductors of heat and electrical energy, they are malleable (can be flattened into shapes) and ductile (can bend). Examples: iron, copper, lead, tin.

• Metalloids – have properties of both metals and nonmetals. Some shiny or dull. Somewhat malleable and ductile. Some can conduct heat or electricity. Examples: silicon, antimony and boron.

• Nonmetals – dull, poor conductors of heat and electricity, tend to be brittle and unmalleable. Examples: sulfur, bromine, neon

Families of the Periodic Table

Atoms

• The smallest particle of a substance is an atom. Every element is made of its own unique atom (and every atom of that element looks the same).

• Atoms are the source of energy for each substance. Each atom has a “brain” (nucleus) that helps to control the behavior of the atom.

A Group of Gold Atoms

http://www.youtube.com/watch?v=p9dn-Umr7VU

Parts of the Atom

• Inside the nucleus:• Protons – positive (+) charge, the number

can never change, because they can’t leave the nucleus.

• Neutrons – neutral charges inside the nucleus that 1) add mass to the atom, and 2) keep the protons from repelling.

Traveling Negative Charges

• Electrons – located in shells (pathways) outside the nucleus, these are the only particles that can cause an atom to join with another atom.

• Electrons “hang around” the outside of the atom because they are attracted to the positive force of the protons. However, the further away an electron is from the protons, the more likely they are to leave.

Electron Cloud

• http://www.youtube.com/watch?v=IPdO-NIUuEo&feature=related

Atoms

Molecules

• A molecule is formed when the atoms share an electron.

• Example:• H20 = 1 molecule of water

• 2H20 = 2 molecules of water

• NaCl = 1 molecule of table salt• 4NaCl = 4 molecules of table salt

Compounds

• A compound is a pure substance made of

two or more different elements that are chemically combined. There must be a reaction to create a substance different from the two elements, and another chemical reaction to undo it.

• Examples: iron + oxide = iron oxide (rust). Sodium + chlorine = sodium chloride (table salt).

Compounds: 2 Hydrogen + 1 Oxygen = Water

The Unique Properties of Compounds

• Just like elements, compounds have their own physical properties (melting point, boiling point, density, color, etc.). They can also be identified by their chemical properties.

• Because a compound is a different substance than the elements that make it up, then a compound has different properties. Chlorine by itself is poisonous, but not when it combines with sodium to become NaCl (table salt).

Iron Oxide (rust)

Compounds and Simpler Substances

• Unlike elements, compounds can be broken down into simpler substances, but only through chemical changes. For example adding energy (heat or electrical) can break down a substance into it’s original elements. Carbonic acid (in drinks like cola) can be added to water molecules, which then could be broken down into the elements of carbon, oxygen and hydrogen.

Mixtures

Mixtures

• A mixture is a combination of two or more substances that are not chemically bonded. Mixtures are a physical change.

- Mixtures retain their identity – Each substance in a mixture has the same chemical makeup it had before the mixture formed.

- Mixtures can be physically separated – It isn’t always easy, but you can separate the substances (see the ways on page 91).

Mixtures (continued)

• The components of a mixture do not have a definite ratio – Since there is no chemical bonding, the components of a mixture do not have to combined into a definite ratio. For example, air is a mixture of gases, but not all a the same ratio.

Compounds vs Mixtures

Compounds

- Are made up of elements

- They lose their original properties

- Can only be separated by chemical means

- Formed using a set mass ratio of components

Mixtures- Made up of elements,

compounds or both- These components

keep their original properties

- Separated by physical means

- Form using any ratio of components.

Compounds vs Mixtures

Solutions

• A solution is a mixture that appears to be a single substance but is composed of particles of two or more substances that are distributed evenly amongst each other.

• When dissolving, the solute is the substance that is dissolved, and the solvent is the substance in which the solute is being dissolved. Ex: Kool Aid (solute) dissolves in water (solvent). Water is called the universal solvent.

Creating a Solution

• http://www.youtube.com/watch?v=hydUVGUbyvU&feature=related

Solution of Ice Tea (Sugar, Tea and Water)

Concentration: How Much Solute is Dissolved?

• Concentration is the amount of solute dissolved in a solvent.

• This can be expressed in grams/milliliters (yep, it’s the density of the solution!)

• Solutions can be concentrated, a high amt of g per ml (g/ml) - or diluted, a low amt of g per ml (g/ml)

• EX: Concentration – 1pkg Kool Aid to 4 tspns water (strong.) Diluted: ½ pkg Kool Aid to 3 gal of water (weak.)

Different States of Solutions

1. Gas in gas: gasses in dry air2. Gas in liquid: soft drinks (CO2 in water and

syrup)

3. Liquid in liquid: antifreeze (alcohol in water)

4. Solid in liquid: salt water5. Solid in solid: alloys – metals and

nonmetals dissolved in other metals. Example: brass (metal zinc melted in copper).

Water is SO special!• Ocean water is a solution

of many substances: solids, liquids, and gases all dissolved in water.

• Your blood and body fluids are water solutions of sugars, ions, and minerals.

• Water dissolves so many more things than other solvents that it is called the universal solvent.

Solubility

Solubility

• The amount of a substance that can be dissolved is its solubility. For example, if you add too much sugar to water, then the extra sugar won’t dissolve (but will drop to the bottom of the glass).

• Most solids increase solubility in liquids when heat energy is added (adding sugar to hot water dissolves more sugar).

What affects how fast solids will dissolve?

• Temperature! If you increase temperature, solids will dissolve faster.

Movement! If you stir them, solids will dissolve faster!

Particle size! The smaller the particles, the greater the surface area so the faster they will dissolve.

What affects how much will dissolve?

• Solubility of most solids in a liquid increases when you raise the temperature!

• Solubility of a gas in a liquid decreases when you raise the temperature!

• Gases are also affected by pressure. As you increase the pressure, more gas will dissolve. Soft drinks are canned or bottled under pressure so more CO2 can be dissolved in the solution.

http://www.youtube.com/watch?v=M8sAYedRHO8&feature=related

(Stop at 2:18!)

Homogeneous Mixture

• Some mixtures look the same throughout (you can’t tell one ingredient from another.)

• Examples would be ice tea, chocolate milk, or anything that could dissolve into another liquid or gas.

Homogeneous Mixtures

Suspensions

• In some solutions, the particles in a mixture can settle out and been seen while in still in the solvent. They don’t dissolve, but are suspended in the liquid. For example: a snow globe.

• Heterogeneous mixture – you can see the different components in the mixture (salad dressing). The particles that separate are large enough to scatter or block light.

• These suspensions can be separated using a filtration system.

Heterogeneous Mixtures

Colloids• A colloid is a mixture that has properties of

both a solution and a suspension. The particles are dispersed throughout , but they aren’t heavy enough to settle out. The particles can’t settle, but they are large enough to scatter light. Unlike a suspension, a colloid cannot be separated by filtration. Milk, mayonnaise, Jello and whipped cream are examples of colloids.

Suspensions and Colloids Experiment

• http://www.youtube.com/watch?v=q96ljVMHYLo

Colloids

Acids and Bases

• Acids are water solutions that contain the element hydrogen (with a positive + charge.)

Acids and Bases

1) Acids are substances that have positively charged Hydrogen particles (hydronium ions).

2) They have a sour taste, can be corrosive (burn skin), and are often found in food.

3) Acids turn blue litmus paper red.

4) On a pH scale, acids are found between 1 (strong) to 6 (weak.)

Bases

1) Bases contain HO- substances.

2) Bases have a “bitter” taste. However, they aren’t as common in food (household cleaners.)

3) Bases are often used in detergents and cleaners.

4) Bases turn red litmus paper blue. On the pH scale, bases are between 8 (weak) and 14 (strong).

Acids and Bases Song

• http://www.youtube.com/watch?v=zTLiJE-j1-I