How Have Ideas About Atoms Changed?

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1 WHAT ARE ATOMS?

2 What are Atoms? Atoms- The smallest particles of an element that have the same chemical properties as the element. The atoms of one element are different from the atoms of another element. Each element is made up of a particular type of atom and has its own special properties. Atoms are so small that billions of atoms fit on the head of a pin.

3 The Parts of an Atom Nucleus- the densest part of the atom, where most of its mass is. The rest of the atom is just empty space. Inside the nucleus are: Protons- have a positive electric charge Neutrons- have no electric charge. The atomic mass (amu) is the sum of the atoms protons and neutrons. Electrons-have a negative electric charge. They are smaller than protons and they circle around the nucleus. They are held near the nucleus by an attraction to the protons. An atom has equal numbers of protons, neutrons, and electrons

4 How Have Ideas About Atoms Changed? John Dalton proposed that atoms were solid like marbles and had no particles inside J.J. Thompson showed that atoms contained electrons. He proposed that electrons were sprinkled in positively charged fluid Earnest Rutherford and H.G.J Moseley showed that positive matter in atoms was packed into a tiny nucleus Scientists have thought of electrons as clouds surrounding the nucleus.

5 Elements All things around us are made with just a few kinds of matter. Each kind of matter has its own set of properties. There are over 100 basic kinds of matter called elements. Elements are the basic building block of matter. They combine to make up all other kinds of matter. They cannot be broken into smaller pieces with ordinary physical or chemical processes. More than 75% of the elements are called metals. Metals are shiny, bendable, and able to conduct heat energy and electricity well.

6 Periodic Table of Elements This contains all of the known elements. Elements can be combined to make other things For example, hydrogen and oxygen combine to make water.

7 Element properties Each element has its own set of chemical and physical properties Chemical properties describe how a material changes into other materials Physical properties can be measured without changing the material Examples: color, odor, mass, volume, Density, texture, Magnetism and hardness. These properties do not change.

8 What is the Periodic Table? Dmitry Mendeleyev tried to arrange the elements in a different way. He discovered the modern periodic table of elements. He arranged them by atomic mass a discovered a repetitive pattern of several properties (density, metal character, and ability to react with other elements). Why was he so successful? He left blank spaces in the table when necessary to keep the periodic pattern. He predicted that elements would be discovered to fill them. He was correct. Eventually other atoms were discovered that filled in the blanks.

9 More About Mendeleyev

10 Reading the Periodic Table The elements in the periodic table are arranged in order of increasing atomic number. Atomic Number- atoms in each element has a unique number of protons. Thus number is used to classify the atom. Families- the vertical columns contain elements that react with other substances in similar ways. Period- each row of elements. According to their properties, elements can be placed in one of three groups. Metals- conduct heat and electricity, are shiny when polished, and bend instead of break. Metalloids- have only some properties of metals. Nonmetals- the opposite of metals.

11 What Are Metals, Nonmetals, and Metalloids? About ¾ of the elements are metals. Metals conduct electricity. Example- Copper is used in electrical wiring. Nonmetals tend to have the properties opposite of metals. They are poor conductors of electricity. They are normally solids of gases at room temperature. Solid nonmetals are brittle instead of bendable. Metalloids properties fall between metals and nonmetals. Used to make computer chips and circuits. Silicon is a metalloid and is used in computer chip and found in sand.