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Atoms What are atoms? An atom is the smallest piece of an element. It is one million times smaller than the width of a piece of hair. Each type of atom represents a different element on the Periodic Table. All matter is made of atoms. What are the main sections of an atom? What are the parts of an atom? Where can each part be found? An atom has a nucleus in the center surrounded by the electron cloud. An atom has three parts: protons, neutrons and electrons. Protons and neutrons are found in the nucleus. Electrons whiz around outside of the nucleus in the electron cloud. Atoms Each atom is different because of the number of protons it has. This is called the atomic number. Atoms are arranged on the Periodic Table by their atomic number, or, by the number of protons in the nucleus. Sodium – soft, silver metal that can be cut with a butter knife and explodes when in contact with water Chlorine – pale, green, poisonous gas that was used in chemical warfare in the past Does an atom have mass? Atoms are so small that their mass is measured in atomic mass units, amu. Each proton is 1 amu. Each neutron is 1 amu. An electron is 0 amu. Where is most of the mass of an atom? 0 amu 1 amu 1 amu It’s Time for Atomic Math!!!!!!!!! Atomic Mass The mass of an atom is in its nucleus. The mass is equal to the number of protons and neutrons. Protons + Neutrons = Atomic Mass Atomic Mass The number of neutrons in an atom is not given on the Periodic Table. To determine the number of neutrons you round the atomic mass and subtract the atomic number. Atomic Mass atomic mass – atomic number = number of neutrons rounded (protons + neutrons) – protons = neutrons Atomic Mass Examples Sodium, Na, is atomic #11 and has a mass of 22.98 amu 23 – 11 = 12 neutrons Chlorine, Cl, is atomic #17 and has a mass of 35.45 amu 35 – 17 = 18 neutrons Does an atom have charges? Protons are positive (+) Neutrons are neutral (0) Electrons are negative (-) Is the nucleus charged? Is the electron cloud charged? - + 0 Does an atom have charges? Protons are positive (+) Neutrons are neutral (0) Electrons are negative (-) The nucleus is positive. The electron cloud is negative. Because an atom has the same number of + protons and - electrons, an atom is neutral. - + 0 Electron Clouds The electron cloud is the area surrounding the nucleus. The electrons whiz around here. Most of the area is empty space! Electrons are arranged into energy levels called orbitals. When the orbital is full, it is said to be complete. Electron configuration – You’ll see this in high school and beyond Electrons fit into the energy levels or orbitals around a nucleus in specific patterns. This arrangement is called the electron configuration and it is given on the Periodic Table. If you add the numbers in the electron configuration, the sum is the total number of electrons, which is equal to the atomic number! Electrons farther from the nucleus have more energy. Valence Electrons Electrons in the orbital farthest from the nucleus are called valence electrons. These electrons form chemical bonds with other atoms and give elements their chemical properties. Atoms combine with other atoms to complete their outermost or last energy level, called the valence orbital. Atoms want their last orbital to be complete. It makes the atom stable. Lewis Dot Structure: A Lewis dot structure is like a simplified electron energy level model. The Lewis structure contains the element symbol with dots representing electrons. The only electrons shown are those on the outer energy level or valence electrons. The electrons are placed around the element symbol, one at a time, clockwise or counterclockwise, and then grouped in pairs as more electrons are added. Stop here for today!!! More on Atoms Because atoms have the same number of positive protons and negative electrons, atoms are neutral. They have no charge. If an atom loses or gains electrons, it is called an ion. An ion is a charged particle. Ions If an atom loses an electron (-), would it be a positive or negative ion? Ions If an atom loses an electron (-), would it be a positive or negative ion? Positive because you are taking away a negative charge so there are more protons than electrons Example: Sodium has 11 protons and 11 electrons. If it loses an electron, it has 11 positive protons but only 10 negative electrons. Ions If an atom gains an electron (-), would it be a positive or negative ion? Ions If an atom gains an electron (-), would it be a positive or negative ion? Negative because you are adding a negative charge so there are more electrons than protons Example: Chlorine has 17 protons and 17 electrons. With an additional electron, chlorine has 17 positive protons and 18 negative electrons. What happens to opposites? Ions Lewis structure with Na and Cl