2 ObjectivesExplain the relationship between matter, atoms, and elementsDistinguish between elements and compoundsDescribe molecules, and explain how they are formedInterpret and write some common chemical formulasCategorize materials as pure substances or mixtures
3 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.
4 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 elementCompound: 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.
6 The human body is composed of living cells, which in turn contain large moldecules and compounds made up of elements.
7 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.
8 Remember: some elements occur singly in nature Ex) NeonThe atoms of other elements combine to form polyatomic moleculesEx) O2 H P4
9 Molecules can be represented by: FormulaPhysical modelsChemical formula- a combination of chemical symbols and numbers to represent a substanceC16 H10 N2 O2 IndigoC8 H10 N4 O2 Caffeine
10 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
11 Solids can mix with liquids Mixtures can be separated into their componentsHeterogeneous mixture- substances aren’t mixed uniformly and are not evenly distributedEx) flour in water – a suspensionHomogeneous mixture- components are evenly distributed, mixture is same throughoutEx) sugar in water
12 Liquids can mix with liquids Gasoline is a liquid mixture of ~ 100 liquidsComprised of miscible liquidsMiscibility- only miscible liquids that are combined (ex. Ethylene glycol and water) can dissolve in each other.They form a solution (a homogeneous liquid mixture)
13 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.
14 Gases can mix with liquids Ex) LavaThe 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
15 2.2ObjectivesDistinguish between the physical and chemical properties of matter, and give examples of eachPerform calculations involving densityExplain how materials are suited for different uses based on their physical and chemical propertiesDescribe characteristic properties
16 Physical propertiesPhysical properties identify things by describing matterExamples:ColorShapeHeightMassVolumedensity
17 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)StrengthHardnessAbility to conduct electricityMagnetismHeat
18 . 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 samesubstanceMelting pointº CelsiusBoling pointC35504827Au10632970Fe15352750Hg-39357N-209-196O-218-183NaCl8011413H2O100.
19 Density= MassVolumeDensity depends on the arrangement of atoms within that sample of matterDensity determines whether an object will float or sink
20 Densities of some substances Chemical formulaDensity in g/cm3Air, dryMixtureBrick1.9Gasoline0.7HeliumHeIceH200.92IronFe7.86LeadPb11.3NitrogenN2Steel7.8Water1.00
21 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
22 Chemical PropertiesChemical 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 rustFlammability (ability to burn)
23 Changes of matter Objectives: Explain physical change, give examples Explain chemical change, give examplesCompare and contrast physical and chemical changesDescribe how to detect whether a chemical change has occurred
24 A physical change affects one or more physical properties of a substance without changing its identityEx) breaking chalkGetting a hair cutDissolving sugarMelting iceSanding woodCrushing a canMixing oil and vinegar
25 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
26 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
27 Changes in the state of matter are physical because they do not change the identity of the substance!!!
28 Chemical changesA 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 pennycopper carbonate)Oxidation- (iron rust)Fruits ripeningFood being digested
29 Chemical changes form new substances that have different properties Ex) baking a cake
30 Chemical changes can be detected Clues suggesting that a chemical change occurred:Change in odor or colorFizzingFoamingProduction of: sound, heat, light, odor
31 Chemical changes cannot be reversed by physical changes Ex) you can not unbake a cakeHowever, some chemical changes can be reversed under the right conditions by other chemical changes.