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

Applies to single or small number of events Applies to all events Describes what happens observationlaw Explains why things happen hypothesistheory

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 Substance Constant Composition Mixture Variable 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

 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 78 o C 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 Theory Dalton’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 Theory Dalton’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 Atom Plum 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 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