chemistry - investigates and explains: structure and properties/behavior of matter matter = anything...

Chemistry - investigates and explains:• structure and • properties/behavior of matter

Matter = anything that takes up space and has mass = everything around you

Matter is made up of atoms

Mass = amount of matter that an object contains

What is Matter?

properties = characteristics and behavior of matter (includes changes that matter undergoes).

What color is it?Is it solid, liquid or gasIs it reactive?

structure = composition

• what matter is made of

• how matter is organized.

How do we classify matter?

So how do figure out what matter is made of?

Macroscopic View = large enough to be seenokay for general properties like color,

state, conductivity, etc.

Submicroscopic View - too small to be seen by even a microscope

good for finding out true structure

To visualize the submicroscopic view we create models

***Differencences in behavior are due to different arrangement of atoms

sucrose and aspirin are both composed of carbon, hydrogen, and oxygen

aspirin sucrose

Classifying matter

• What is it made of?

qualitative observation is one that can be made without measurement

describes color, odor, shape, or some other physical characteristic that relates to the five senses

how much of each of the elements is present?

A quantitative observation is one that uses measurement = numerical data.

Classifying matter

• Examples of the physical properties of a chunk of matter include its:

• solubility, - dissolves in water?

• melting point,

• boiling point,

• color,

• density,• electrical conductivity,

• and physical state (solid, liquid, or gas).

• A physical change is a change in matter that does not involve a change in the chemical identity of individual substances.

• Examples of physical changes include:

• boiling, • freezing

, • melting,

• evaporating, • dissolving, • and crystallizing.

Classify by purityIs it a pure substance or mixture?

Pure substance = sample of matter, either a single element or a single compound that has definite chemical and physical properties

Classifying Matter

substance is not changed = no fixed composition

the basic identity of each

Mixture = made up of different kinds of matter

Pure Substance or Mixture?

heterogeneous mixture is one with different compositions, depending upon where you look

Pure Substance or Mixture?

• Homogeneous mixtures are the same throughout.

• Another name for a homogeneous mixture is solution.

Pure substance or a mixture?

• When you dissolve sugar in water, sugar is the solute—the substance being dissolved.

• The substance that dissolves the solute, in this case water, is the solvent.

• When the solvent is water, the solution is called an aqueous solution.

Pure substance or a mixture?

• Alloys are solid solutions that contain different metals and sometimes nonmetallic substances.

Pure substance or a mixture?

compound = pure substance that can be broken down into simpler substances.

element = substance that cannot be broken down into simpler substances.

Element or Compound?

salt

gold

compound is a chemical combination of two or more different elements joined together in a fixed proportion with a unique set of chemical and physical properties

Compounds

Compounds Are More Than One Element

• The properties of the compound are different from the properties of the elements that compose the compound.

silver + bromine = silver bromide

Compounds Are More Than One Element

• A formula is a combination of the chemical symbols that show what elements make up a compound and the number of atoms of each element.

Compound Formula

Caffeine C8H10N4O2

States of Matter

• Most matter on Earth exists in one of three physical states: solid, liquid, or gas. A fourth state of matter, called plasma, is less familiar.

• Changes in state are examples of physical changes because there is no change in the chemical composition identity of the substance.

• Ice can melt back to form liquid water, and steam will condense on a cool surface to form liquid water.

States of Matter

• Some substances are described as volatile, which means that they change to a gas easily at room temperature.

• Alcohol and gasoline are more volatile than water.

• Density is the amount of matter (mass) contained in a unit of volume.

Density is measured in units of grams (mass) per milliliter (volume) or g/mL

Density

• Styrofoam has a low density or small mass per unit of volume.

Stones have a large density or a large mass per unit of volume

Density

Chemical Properties• Chemical properties are those that can

be observed only when there is a change in the composition of the substance.

• Rusting is a chemical reaction in which iron combines with oxygen to form a new substance, iron oxide.

• Inability to react is also a chemical property.

Physical Chemical

density Reactivity / stability

Melting/freezing point

color Flamablility

conductivity

solubility

Physical vs. chemical properties

Physical change = NO change in composition

Chemical change = change in chemical composition

Below are listed changes that can be observed in everyday life. Tell whether it is a physical change or a chemical change. Then explain the basis on which you made your decision.

1. an icicle melting2. charcoal burning3. magnetizing a piece of steel4. iron rusting5. rubbing alcohol evaporating from the

skin

Chemical Changes

chemical change, the change of one or more substances into other substances.

• A chemical property always relates to a

• Another term for chemical change is chemical reaction.

chemical change involves only a rearrangement of the atoms. Atoms do not just appear or disappear.

******Law of Conservation of Mass****** In a chemical change, matter is neither created nor destroyed. aka: the law of conservation of matter.

Chemical Reactions

Chemical Reactions and Energy

• All chemical changes also involve some sort of energy change.

• Energy is either taken in or given off as the chemical change takes place. Energy is the capacity to do work.

• Work is done whenever something is moved.

Chemical Reactions and Energy

• Energy is also produced and released in the form of heat and light.

• Chemical reactions that give off heat energy are called exothermic reactions.

• Chemical reactions that absorb heat energy are called endothermic reactions.

Chemical Reactions and Energy

Identify each of the following as either a compound or a mixture.

A. sand

B. water

C. juice

Answers

A. sand

B. water

C. juice

mixture

compound

mixture

Classify each of the following as a chemical or physical property.

A. density

B. reactivity

C. color

D. melting point

Answers

A. density

B. reactivity

C. color

D. melting point

physical propertychemical property

physical propertyphysical property

Scientific Method –

answer a question or study a situation

• A typical scientific method includes:

• making observations,

• forming a hypothesis,

• performing an experiment,

• and arriving at a conclusion.

A hypothesis is a possible explanation for what has been observed

An experiment is a set of controlled observations that test a hypothesis

Scientific Method

Scientific Methods

• The variable that is changed in an experiment is called the independent variable.

• The variable that you watch to see how it changes as a result of your changes to the independent variable is called the dependent variable.

Scientific Methods

• Many experiments also include a control, which is a standard for comparison.

• A conclusion is a judgment based on the data obtained in the experiment.

A student tests the ability of a given chemical to dissolve in water at three different temperatures.

independent variable: temperature;

dependent variable: ability to dissolve in water

Answer 1a

Question 1a

A farmer compares how his crops grow with and without phosphorous fertilizers.

independent variable: presence of phosphorous fertilizer;

dependent variable: crop growth

Answer 1b

Question 1b

a. alloy h. law of conservation of massb. aqueous solutions i. massc. chemical property j. matterd. compound k. physical changee. energy l. propertiesf. exothermic m. quantitativeg. formula n. solute

MatchingMatch each item with the correct statement below.____ 29. The type of change in which the identity of substances does not change.____ 30. A chemical combination of two or more elements joined together in a fixed proportion.____ 31. The fact that matter can be neither created nor destroyed in a chemical change.____ 32. Solutions in which water is the solvent.____ 33. The behavior of matter and its characteristics.____ 34. A solid solution usually consisting of two or more metals.____ 35. Any chemical reaction that gives off energy.____ 36. The combination of chemical symbols that describes the composition of a chemical compound.____ 37. The measure of the amount of matter that an object contains.____ 38. An observation that makes use of measurement.____ 39. Can be observed only when there is a change in composition of a substance.____ 40. Anything that takes up space and has mass.____ 41. The material that is dissolved in a solution.____ 42. The capacity to do work.