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Introduction to Atoms Chemistry Standard 1 a: Essential Question: How is an element’s position on the periodic table related to its atomic number and atomic mass? 1 I. Atoms A. Tiny particles that make up all matter. B. Contain three smaller subatomic particles: protons, neutrons, & electrons. C. Have two parts: 1. Nucleus 2. Electron cloud. 2 II. Atomic mass 1. Atoms have a VERY SMALL mass. 2. An atom’s mass is measured in atomic mass units (amu) -27 3. 1 amu = 1.66 x 10 kg 4. The mass of an atom is found on the periodic table. 1. What is Carbon’s mass? a. 12.01 amu 3 III. Protons and neutrons 1. The nucleus is the center of the atom. 2. Protons and neutrons are found in the nucleus. 3. Protons have a positive charge. 4. Protons are very large (compared to electrons) a) A proton’s mass is about 1.00 amu (1840 times greater than the mass of an electron!) 4 5)Neutrons have no charge 6)Neutrons have an mass of 1.00 amu. 5 IV. Electrons 1. Electrons are found outside the nucleus, in the electron cloud. 2. Electrons have a negative charge. 3. Electrons are VERY small 6 V. Atomic number 1. Protons are positively charged and electrons are negatively charged. 2. Atoms are neutral (they have no charge). a) Each atom must have the same number of protons and electrons so their charges cancel each other. 7 3. The atomic number is the number of protons. A.If an atom is neutral, the number of electrons is the same as the atomic number. B. Atoms of the same element have the same atomic number. 8 C. The atomic number is found on the periodic table. D. To Symbolize the atomic number … atomic number element’s symbol 9 VI. Mass number 1. (Or the atomic mass) is the number of protons + the number of neutrons. + 0 a) atomic mass = #P + #N 2. You can find the #of neutrons by subtracting # of protons from atomic mass 10 3. The mass number (atomic mass) is found on the periodic table. 4. The mass number can be written with the element’s symbol… A. C-12 mass number B. . atomic number element’s symbol 11 5. Atoms of the same element: A. Can have different mass numbers (called isotopes): C-12, C-14 B. Must have the same number of protons BUT they can have a different number of neutrons. 12 6. Atoms with the same number of protons and electrons but different numbers of neutrons are called isotopes. 7. The atomic mass of an element is an average mass of the atoms in a naturally occurring sample of the element. 13