A MATTER OF FACT Introduction to Elements, Atoms, and the Periodic Table

WHY ISN’T IT A GOOD IDEA TO CLASSIFY MATTER BY ITS PHASES?  Because one kind of substance can exist in more than one phase (such as H 2 0 can be ice, water, or steam) and matter changes phases rather easily.

WHY ISN’T MATTER CLASSIFIED ACCORDING TO ITS PHYSICAL CHARACTERISTICS, SUCH AS COLOR?  Scientists would not find it very useful to group sunflowers, gold, and the sun together.

ELEMENTS, COMPOUNDS, & MIXTURES  Scientists like to classify things.  One way that scientists classify matter is by its composition (what it’s made of)  All matter can be classified as one of three categories: elements elements compounds compounds mixtures mixtures

ELEMENTS  Elements are the simplest pure substances.  An element cannot be broken down or separated into simpler substances by physical or chemical means.  Elements are the building blocks of all materials.  About one hundred elements can combine in different ways to form millions and millions of different substances!

ELEMENTS AND ATOMS  Elements are made of particles.  Elements are pure substances.  All of the particles that make up an element are exactly alike.  The smallest particle into which an element can be divided and still be the same substance is called an… Atom

PARTS OF THE ATOM  Atoms are made of three different types of particles:  Proton – Positively charged (+)  Neutron – No charge (neutral)  Electron – Negatively charged (-)  Nucleus – Center of the atom  Made of protons and neutrons  Electrons are constantly moving around the nucleus.

PARTS OF THE ATOM

ELEMENTS AND THEIR SYMBOLS  In 1813, a system of symbols representing the elements was introduced.  Each symbol consists of one or two letters.  Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used.

COMMON ELEMENTS AluminumAl BromineBr CalciumCa CarbonC GoldAu HeliumHe HydrogenH NitrogenN

PERIODIC TABLE

CLASSES OF ELEMENTS  Metals  Most of the elements on the periodic table are metals.  Metals tend to be solids that are shiny, malleable, ductile, and good conductors of electricity.  Nonmetals  More than half of the nonmetals are gases.  Nonmetals typically are not shiny, not malleable, not ductile, and are poor conductors of electricity.  Metalloids  Metalloids are also known as semiconductors.  Metalloids have some properties of metals and some of nonmetals.