What is Matter?

Objectives Explain the relationship between matter, atoms, and elements Distinguish between elements and compounds Describe molecules, and explain how they are formed Interpret and write some common chemical formulas Categorize materials as pure substances or mixtures

What is chemistry and matter? Chemistry: the scientific study of the composition, structure, and properties of matter and the changes that matter undergoes. Matter: anything that has mass and takes up space.

Element: a substance that cannot be separated or broken down into simpler substances by chemical means. Atom: the smallest unit of an element that maintains the properties of that element Compound: a substance made of atoms of two or more different elements that are chemically combined. The word atom is derived from the Greek word, a means not , tomos means cutting. Literally meaning indivisible.

The human body is composed of living cells, which in turn contain large moldecules and compounds made up of elements.

Molecule: the smallest unit of a substance that keeps all of the physical and chemical properties of that substance. A compound is made of two or more different elements, but a molecule may be of the same elements or different elements.

Remember: some elements occur singly in nature Ex) Neon The atoms of other elements combine to form polyatomic molecules Ex) O2 H2 P4

Molecules can be represented by: Formula Physical models Chemical formula- a combination of chemical symbols and numbers to represent a substance C16 H10 N2 O2 Indigo C8 H10 N4 O2 Caffeine

Mixture- a combination of two or more substances that are not chemically combined Pure substance- a sample of matter, either a single element or a single compound, that has definite chemical and physical properties *Elements and compounds are pure substances, but mixtures are not

Solids can mix with liquids Mixtures can be separated into their components Heterogeneous mixture- substances aren’t mixed uniformly and are not evenly distributed Ex) flour in water – a suspension Homogeneous mixture- components are evenly distributed, mixture is same throughout Ex) sugar in water

Liquids can mix with liquids Gasoline is a liquid mixture of ~ 100 liquids Comprised of miscible liquids Miscibility- only miscible liquids that are combined (ex. Ethylene glycol and water) can dissolve in each other. They form a solution (a homogeneous liquid mixture)

Immiscible- liquids such as oil and water or toluene and water that are practically insoluable Instead, they form two layers, with the denser liquid on the bottom.

Gases can mix with liquids Ex) Lava The molten rock in some types of volcanoes contains large quantities of gas. Pumice, a solid foam that occurs naturally on Earth, is a volcanic rock formed by the violent separation of these extremely hot gases from lava. As the exploding lava cools, it traps the bas bubbles. Some pumice is so soft that it is spongy, and has such a low density that it floats on water

2.2 Objectives Distinguish between the physical and chemical properties of matter, and give examples of each Perform calculations involving density Explain how materials are suited for different uses based on their physical and chemical properties Describe characteristic properties

Physical properties Physical properties identify things by describing matter Examples: Color Shape Height Mass Volume density

More examples of physical properties: Melting point (temperature and pressure at which a solid becomes a liquid) Boiling point (temperature and pressure at which a solid becomes a liquid) Strength Hardness Ability to conduct electricity Magnetism Heat

. substance Melting point º Celsius Boling point C 3550 4827 Au 1063 A characteristic of any pure substance is that its boiling point and melting point are constant if the pressure remains the same substance Melting point º Celsius Boling point C 3550 4827 Au 1063 2970 Fe 1535 2750 Hg -39 357 N -209 -196 O -218 -183 NaCl 801 1413 H2O 100 .

Density= Mass Volume Density depends on the arrangement of atoms within that sample of matter Density determines whether an object will float or sink

Densities of some substances Chemical formula Density in g/cm3 Air, dry Mixture 0.00129 Brick 1.9 Gasoline 0.7 Helium He 0.00018 Ice H20 0.92 Iron Fe 7.86 Lead Pb 11.3 Nitrogen N2 0.00125 Steel 7.8 Water 1.00

The density of a liquid or a solid is affected only slightly by a change in temperature or pressure. In a gas however, an increase in temperature or a decrease in pressure significantly reduces the density of a gas

Chemical Properties Chemical property- describes how a substance changes into a new substance either by combining with other elements or by breaking apart into new substances. Examples: Reactivity of element with other compounds (oxygen, acid, water, other) Oxidation of Fe creates rust Flammability (ability to burn)

Changes of matter Objectives: Explain physical change, give examples Explain chemical change, give examples Compare and contrast physical and chemical changes Describe how to detect whether a chemical change has occurred

A physical change affects one or more physical properties of a substance without changing its identity Ex) breaking chalk Getting a hair cut Dissolving sugar Melting ice Sanding wood Crushing a can Mixing oil and vinegar

Mixtures can be physically separated because the components are not chemically combined. Distillation device- can separate components of mixtures that have different boiling points. When heated, the component that boils and evaporates first, separates from the mixture and collects in the receiving tank

Magnets can be used to separate mixtures that have components containing iron. Centrifuge- tool used to separate mixtures. It spins a sample of a mixture rapidly until the components of the mixture separate

Changes in the state of matter are physical because they do not change the identity of the substance!!!

Chemical changes A change that occurs when a substance changes composition by forming one or more new substances. Ex) soured milk (produces odor) Effervescent tablets (produce CO2) (copper pennycopper carbonate) Oxidation- (iron  rust) Fruits ripening Food being digested

Chemical changes form new substances that have different properties Ex) baking a cake

Chemical changes can be detected Clues suggesting that a chemical change occurred: Change in odor or color Fizzing Foaming Production of: sound, heat, light, odor

Chemical changes cannot be reversed by physical changes Ex) you can not unbake a cake However, some chemical changes can be reversed under the right conditions by other chemical changes.