ELEMENTS, COMPOUNDS AND MIXTURES

WHAT IS A CHEMICAL ELEMENT?

A C H E M I C A L E L E M E N T, O R A N E L E M E N T, I S A M AT E R I A L W H I C H C A N N O T B E B R O K E N D O W N O R C H A N G E D I N T O A N O T H E R S U B S TA N C E U S I N G C H E M I C A L M E A N S . A N E L E M E N T I S A P U R E S U B S TA N C E M A D E U P O F O N LY O N E T Y P E O F PA R T I C L E . E L E M E N T S M AY B E T H O U G H T O F A S T H E B A S I C C H E M I C A L B U I L D I N G B L O C K S O F M AT T E R . T H E R E A R E 11 7 O R 11 8 K N O W N E L E M E N T S .

WHAT IS THE MOST ABUNDANT ELEMENT?

The most abundant element in the universe is Hydrogen, which makes up about 3/4 of all matter! Helium makes up most of the remaining 25%. Oxygen is the third most abundant element in the universe. All of the other elements are relatively rare.

ELEMENT CHARACTERISTICS

• Consists of only one kind of atom. • Cannot be broken down into a simpler type

of matter by either physical or chemical means.

• Can exist as either atoms or molecules.

A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. Note that the two nitrogen atoms which comprise a nitrogen molecule move as a unit.

THE THREE MAJOR CATEGORIES OF ELEMENTS

Elements are grouped into categories based by their chemical and physical properties.

If you know the categories, you know the properties.

The elements of the periodic table are separated into three basic categories; metals, nonmetals and/or metalloids.

METALS, NONMETALS AND METALLOIDS

Metals

Elements that are shiny, good conductors of thermal energy and electric current, malleable, and ductile.

Nonmetals

Elements that are dull, poor conductors of thermal energy and electric currents. Solid nonmetals tend to be brittle and unmalleable.

Metalloids (semiconductors)

Elements that have properties of both metals and nonmetals. Some are shiny and some can be dull. They are somewhat malleable and ductile. Some conduct thermal energy and electric currents well.

WHAT IS A COMPOUND?

Two or more elements chemically combined. (Note: if a sample of matter is made of atoms of two or more elements joined together, always in the same ratio, then that matter is a compound.)

Example: alcohol (CH₅OH), water (H₂O), salt (NaCl), sugar (C₁₂H₂₂O₁₁) & ammonia (NH₃).

COMPOUND CHARACTERISTICS

• Compounds consists of atoms of two or more different elements bound together.

• Can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means).

• Has properties that are different from its

component elements.

• Always contains the same ratio of its component atoms.

FAMILIAR COMPOUNDS• Table Salt- sodium and chlorine

• Water- hydrogen and oxygen

• Sugar- carbon, hydrogen and oxygen

• Carbon dioxide- carbon and oxygen

• Baking Soda- sodium, hydrogen, carbon and oxygen

WHAT IS A MIXTURE?

Two or more elements or compounds that are blended without combining chemically. It can be mixed in any proportion.

Each part of the matter in a mixture has its own identity (properties).

Mixtures can only be separated by using physical means.

• Example: fabrics, vinegar, soil, rocks, rocks, milk, lemonade

Mixtures can be heterogeneous mixtures or homogeneous mixtures.

• Heterogeneous mixtures- the substances in the kind of a mixture are not spread out evenly. Example: a bottle of liquid salad dressing.

• Homogeneous mixtures- the substances are spread evenly throughout, a homogeneous mixture is called a solution. Example: vinegar (water and acetic acid are mixed evenly throughout). Other examples: sea water, soft drinks, glass

COMMON TECHNIQUES FOR SEPARATING MIXTURES

• Separation by hands, filtration or evaporation

• Distillation- a process that separates mixtures based on their boiling points.

• Magnet- a process that can separate metals from other materials based on whether it attracts or not.

• Centrifuge- a machine that separates mixtures according to their densities.

TYPES OF MIXTURES

Solution- a homogeneous mixture in which one substance (the solute) is dissolved in another substance (the solvent).

Example: salt water (Water, the solvent, plus salt, the solute, produces the solution of salty water.)

Solute is a substance that is dissolved and a solvent is what the substance dissolves in.

Suspension- a heterogeneous mixture in which the particles are large enough to be seen by a microscope or the unaided eye (eventually, they settle out of the mixture).

Example: stirring a teaspoon of dirt in a glass of water.

Colloid- a mixture where the size of particles in the mixture are between those of a solution and a suspension. NOTE: The particles appear evenly distributed.

Examples: fog, cheese, butter, jellies, whipped cream.