Chapter 1

Molecular Reasons

What Is Chemistry? The science that deals with the materials

of the universe and the changes these materials undergo.

The science that seeks to understand what matter does by studying what atoms and molecules do.

What Is Chemistry? Everything is made of tiny pieces called

atoms and molecules.

Scientific Method A process for trying to understand nature

by observing nature and the way it behaves, and by conducting experiments to test our ideas.

Key characteristics of the scientific method include Observation, formulation of Hypotheses, Experimentation, and formulation of Laws and Theories.

Scientific Method

Scientific Method

Applies to single or small

number of events

Applies to all events

Describes what happens observation law

Explains why things happen hypothesis theory

Matter Matter is defined as anything that

occupies space and has mass–things you can see, touch, taste, or smell. Matter is neither created nor destroyed in a

chemical reaction.

States of Matter Matter can be

classified as solid, liquid, or gas based on what properties it exhibits.

Composition of Matter Matter that is composed of only one kind

of atom or molecule is called a pure substance.

Matter that is composed of different kinds of atoms or molecules is called a mixture.

Pure SubstanceConstant Composition

MixtureVariable Composition

Matter

Composition of Matter Pure substance

Element—a substance that cannot be broken down into other substances by chemical methods.

Compound—a substance composed of a given combination of elements that can be broken down into those elements by chemical methods.

Composition of Matter Element: made of one

type of atom. Compound: made of

one type of molecule, or array of ions—more than one type of atom.

Composition of Matter Mixture

Mixtures that are uniform throughout are called homogeneous. Also known as solutions.

Mixtures that have regions with different characteristics are called heterogeneous.

Composition of Matter

Homogeneous—appears to be one substance, all portions of a sample have the same composition and properties.

Heterogeneous—presence of multiple substances can be seen, portions of a sample have different composition and properties.

Composition of Matter

Composition of Matter Classify each of the following as a pure

substance (compound or element) or mixture (homogeneous or heterogeneous). Pure water Gasoline Jar of jelly beans Soil Copper metal

Physical and Chemical Properties Physical Properties are the

characteristics of matter that can be changed without changing its composition. Characteristics that are directly observable.

Physical and Chemical Properties Chemical Properties are the

characteristics that determine how the composition of matter changes as a result of contact with other matter or the influence of energy. Characteristics that describe the behavior of

matter.

Physical and Chemical Properties Classify each of the following as a physical

or chemical property. Ethyl alcohol boils at 78oC Sugar ferments to form ethyl alcohol Salt is stable at room temperature, it does not

decompose 36 g of salt will dissolve in 100 g of water

Physical and Chemical Changes Changes that alter the

state or appearance of the matter without altering the composition are called physical changes.

Physical and Chemical Changes Changes that alter the

composition of the matter are called chemical changes.

Physical and Chemical Changes Classify each of the following as a physical

or chemical change. Sugar fermenting to form ethyl alcohol Dissolving of sugar in water Iron metal melting Iron combining with oxygen to form rust

Atomic Theory Atom: the smallest piece of an element

you can have that retains the characteristics of that element. 116 known: 91 found in nature, others are man

made.

Atomic TheoryDalton’s Atomic Theory Elements are made of tiny particles called

atoms. All atoms of a given element are identical. The atoms of a given element are

different from those of any other element.

Atomic TheoryDalton’s Atomic Theory Atoms are indivisible in chemical

processes. Atoms combine in simple, whole-number

ratios to form molecules or compounds. A given compound always has the exact

same numbers and types of atoms.

The Nuclear Atom

Work done by J. J. Thomson and others proved that the atom had pieces called electrons. Electrons are much smaller than atoms and

carry a negative charge. The atom must also contain positive particles

that balance exactly the negative charge carried by electrons.

The Nuclear AtomPlum Pudding Model Reasoned that the atom

might be thought of as a uniform “pudding” of positive charge with enough negative electrons scattered within to counterbalance that positive charge.

The Nuclear Atom

The Nuclear Atom

The Nuclear Atom The atom contains a tiny dense center

called the nucleus. The nucleus has essentially the entire mass of

the atom and is positively charged. The electrons are dispersed in the empty

space of the atom surrounding the nucleus.

The Nuclear Atom The nucleus has a particle that has the

same amount of charge as an electron but opposite sign. These particles are called protons.

Atoms are neutral, therefore the number of protons must equal the number of electrons.

The Nuclear Atom Most nuclei also contain a neutral particle

called the neutron. A neutron has approximately the same

mass as a proton but has no charge.

The Nuclear Atom

Summary of Topics: Chapter 1

What is Chemistry? Scientific method States of Matter Composition of Matter

Pure substances: compounds and elements Mixtures: homogeneous and heterogeneous

Chemical, Physical properties and changes Dalton’s Atomic Theory Nuclear model of the atom