Elements, compounds and mixtures. WHAT IS AN ELEMENT?

Elements, compounds and mixtures

WHAT IS AN ELEMENT?

An element is…

• material made of just one type of atom

• A substance that can not be separated or broken down into simpler substances by chemical means

What are the 3 most abundant elements that make up the earth?

answer

• Oxygen• Iron• silicon

Composition of the earth

What are 3 most common elements that make up a human being?

answer

• Oxygen• Carbon• hydrogen

Elements that compose a human body

WHAT IS AN ATOM?

atom

• The smallest unit of an element that maintains the properties of the element

WHAT IS A COMPOUND?

Compound

• A substance made of two or more different elements that are combined chemically

• Properties of compounds may not be the same as properties of elements that make them up

Compounds

• Substances composed of 2 or more elements that have been chemically combined

• Glass• Sugar• Water• Salt

compounds in real life

• My gold ring

• Water in a bottle

• Metal cart

• Copper wiring

Elements in real life

• Neon lights

• 24 Karat gold bar

• Oxygen in a scuba tank

WHAT IS A MOLECULE?

Molecule

• The smallest amount of a compound that still retains the qualities of the compound

• 1 molecule of water is composed of 2 hydrogen and 1 oxygen atom

Sugar molecule: Made up of atoms combined in a specific way

• Oxygen atoms are red, gray

• Carbon atoms are white

• Hydrogen are small white with red dots

Water on a molecular level

Comparisons and contrasts

• Element and compound

• Comparison: Both are pure substances

• Contrast: Elements can only be composed of one type atom, Compounds are composed 2 or more types atoms (elements)

Atom and Molecule

• Comparison: The smallest unit that still retains material’s properties

• Contrast: Atom is the smallest unit of an element, Molecule is the smallest unit of a compound. Molecules can be composed of different types of atoms

WHAT IS A PURE SUBSTANCE?

What does it mean to be a pure substance?

• “100% pure Honey” • “100% pure salt or sugar”

Pure substance

• Substance composed of either a single type of element or compound chemically combined

• If a Compound, a pure substance has a fixed composition or proportions of elements

• every molecule of water has 2 hydrogen and one oxygen atom

• All compounds can be written with a chemical formula

Pure Substance

• An amount of matter , either single element or one compound that exhibits distinct chemical and physical properties

• Table Salt (if just made with NaCl) is a pure substance

• Grape Juice is not (Water, Sugars, Vitamins)

WHAT IS A MIXTURE?

Mixture

• A combination of 2 or more pure substance combined physically

• Classified by how thoroughly they are mixed

• Properties of mixture similar to properties of components

Mixtures

• If you can separate the substances, it’s a mixture

• If it has ingredients, it’s a mixture

Types of Mixtures

• Heterogeneous• Homogeneous• Miscible• Immiscible• Alloy

Heterogeneous mixture

• Mixtures with ingredients that do not mix well or stay mixed long

• Examples:

Chocolate syrup and milk

Homogeneous Mixture

• Mixtures that mix very well

• Solutions where substances dissolve well into each other

• Can not visually see any separation of the ingredients

• Examples: Gasoline, Soda

Pure substance and mixtures

• Comparison: both are composed of elements

• Contrast: Pure substance is composed of an element or compound whose composition is fixed. Mixture is composed of a combination of pure substances whose composition can vary

WHAT IS THE DIFFERENCE BETWEEN HETEROGENEOUS AND HOMOGENEOUS MIXTURES?

Heterogeneous and homogeneous mixtures

• Comparisons: both mixtures

• Contrast: Heterogeneous materials do not mix well or evenly. They are easily separated. Homogeneous mixtures do mix well and evenly, not easily separated

Difference…

• Heterogeneous mixtures: are mixtures of 2 or more substances that are not completely soluble (bits of each are seen in mixture)

• Homogeneous mixtures: are mixtures of 2 or more substances that are completely soluble (blend completely, can not tell components)

Miscible mixture

• Extremely homogeneous

• Dissolves completely

• Example: Air

Miscibilitity

• How well substances mix together

• The greater the ability to mix (solubility), the more miscible it is.

• Oil and water are immiscible (insoluble)• Carbon dioxide and water (very soluble)

Immiscible mixture

• Extremely heterogeneous

• Don’t mix well at all

• Examples water and granite

Immiscible Mixture

Gasoline, Soda

Solubility

• Measurement of the ability of one substance (solute) to dissolve into another substance (solvent)

WHAT IS AN ALLOY?

Alloy

• An alloy is a solid homogenous mixture of two or more metals.

• The there is not chemical reaction occurring, and the original materials can be recreated by melting.

• There are thousands of different alloys, and people use them for many different purposes.

Different common alloysAlloy Composition Properties Representative

Uses

Brass, copper, zinc Corrosion resistance Instruments

castings

Bronze copper, tin Good for casting Castings

Pewter tin, copper, lead, antimony

Easy to work with Utensils

Solder tin, lead Low melting point Melted to join metalsurfaces

Stainless steel iron, chromium, nickel

Hard, strong, rustresistance

Machines, utensils