What are the Building Blocks of matter?

Main Idea: all matter is made up of particles called atoms. An atom is the smallest unit of an element. Elements are arranged in the Periodic Table. I.) Atoms A. An atom is the basic building block of matter. B. Atoms consist of a nucleus surrounded by moving electrons. 1. The nucleus is the central part of the atom. a. The nucleus contains two kinds of particles, positively charged protons and uncharged neutrons.

i. Protons and Neutrons have about the same mass. b. Electrons are negatively charged particles. i. An electron’s mass is about 1/2000 the mass of a proton or neutron. c. Almost the entire mass of the atom is the nucleus. i. The nucleus is only about 1/10000 the size of the atom, so most of the atom is “empty space”.

II.) Models of the Atom A.Ancient Greek teacher Democritus believed an atom was the smallest particle of matter. B.In 1897, English scientist J.J. Thomson carried out experiments with a glass tube called a cathode ray tube. 1.Thomson discovered negatively charged particles that we call electrons. 2.Thomson’s idea is called the Plum-Pudding Model. C. In 1911, British Scientist Ernest Rutherford disproved Thomson’s model of the atom. 1. Rutherford realized that each bounced particle must have hit a nucleus – a concentrated positively charged mass at the center.

2. Rutherford devised the nuclear model which states that an atom consists of a positive nucleus surrounded by negative electrons. D. In 1913, Danish scientist Niels Bohr revised the model of the atom. 1. According to Bohr’s model, electrons travel in orbits around the nucleus much like planets travel around the Sun. E. The present day model of the atom describes cloud-like regions, called orbitals, where electrons are most likely to be found.

III.) Ions and Isotopes A. The number of protons in an atom is called the atomic number. B. Neutral atoms have the same number of electrons and protons. C. An atom that has more or fewer electrons than it has protons is called an ion. 1. An ion can have a positive or negative charge. a. Positive ions have fewer electrons than protons b. Negative ions have more electrons than protons.

D. Atoms with the same number of protons may have different numbers of neutrons. Such atoms are called isotopes. 1. The isotopes of hydrogen have special names. 2. All other isotopes are named for the number of particles in its nucleus. a. Carbon-14 has 14 particles in its nucleus (6 protons and 8 neutrons)

IV.) Radioactivity A. Almost all atoms are stable and have existed for billions of years. B. The nuclei of some isotopes are unstable. 1. Isotopes with unstable nuclei are said to be radioactive Their nuclei become stable by giving off particles and energy, which is called radiation.

Mental Note-taking Break

C. There are three different types of radiation, alpha, beta and gamma. 1. Radiation can be harmful to humans and other living organisms. 2. Alpha particles can be stopped by paper. 3. Beta particles are able to pass through paper, but not a sheet of aluminum. 4. Gamma radiation has the most energy and is therefore the most dangerous. a. A thick block of concrete or lead is needed to stop it.

V.) Classifying Elements A. An element is a substance that cannot be broken down into other substances. 1. An atom is the smallest unit if an element. a. All atoms of an element contain the same number of protons. 1. Add or subtract a proton and you have a different element. B. Scientist often classify elements based on their properties. 1. Metals are shiny and conduct electricity and heat well. a. They are easily shaped into sheets of wire.

2. Most nonmetals have a dull luster and are poor conductors of electricity and heat. a. They are not easily shaped and may shatter when hit with a hammer. 3. Semiconductors have properties between metals and nonmetals. C. Scientists also classify elements according to state of matter, meaning whether they are solids, liquids or gases at room temperature. D. Elements can be described by many other physical properties including their color, odor, and density. 1. Density is the mass per unit volume of a substance.

E. In 1869, Russian chemist Dmitri Mendeleyev arranged the 63 then known elements according to each elements mass. 1. This was the first periodic table that showed relationships across rows and columns of elements instead of in small groups. VI.) The Periodic Table A. Each box in the table represents one of the elements. 1. The box lists the atomic number, chemical symbol, and name of the element. a. The symbol is a one or two letter abbreviation for the element. Ex: Carbon = C, Iron = Fe (pg’s E12 and E13 in your book)

B. Using the color Key you can tell whether an element is a metal, nonmetal, or semiconductor and whether it is a solid, liquid or gas. C. Unlike Mendeleyev’s table the elements in today’s table are arranged by their atomic numbers. 1. As you move across each row from left to right, the atomic number increases. a. Rows are called periods. D. Metals are mostly on the left side of the table and nonmetals are on the right. Semiconductors are located in between.

E. Today, scientists have have identified 114 elements. 63 are naturally occurring. VII.) Elements in a Column A. Elements are arranged in columns called groups. 1. Elements in any one group have similar chemical properties.