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Inside an Atom Section 3.1 Parts of an Atom 1. Inside Nucleus I. II. 2. Protons-positive charge Neutrons-no charge Outside Nucleus I. Electrons-negative charge Atomic Number Every atom of a particular element contains the same number of protons Ex. Every carbon atom has six protons Atomic Number=The number of protons of an atom Every atom has a unique atomic number Atomic Mass Atoms are too small to measure their mass with everyday units. So instead the atomic mass unit (amu) is used to measure an atom’s mass. Proton≈1 amu Neutron≈1amu 2000 electrons ≈1amu Atomic Mass The mass of an atom is determined by its number of protons and neutrons since electrons weigh very little All atoms of an element have the same number of protons, but can have different number of neutrons Ex. Carbon has 6 protons, but can have 5, 6, 7, or 8 neutrons Neutrons do not play a role in chemical reactions so their numbers do not effect the properties of elements The atomic mass given on the periodic table is the average mass of an element’s atoms Charge of an Atom The number of protons always equals the number of electrons Atoms have a neutral charge because the protons and neutrons neutralize each other electron neutron proton The role of electrons Electrons move around the nucleus so fast that it is impossible to know exactly when any electron is at a particular time Think about the blades of a fan, but in 3 dimensions Most of an atom’s mass comes from the nucleus (Protons, neutrons), but most of its volume comes from the space through which electrons move (baseball field) Valence Electrons Valence electrons are the electrons in the outer layer (furthest distance from nucleus) Valence electrons are very important because they are involved in the formation of chemical bonds A chemical bond forms between two atoms when valence electrons move between them. The valence electrons may be transferred (moved) from one atom to another or shared between atoms. Valence Electrons The number of valence electrons in an atom can range from one to eight Each element has a typical number of valence electrons To the right is a electron dot diagram which shows the number of valence electrons in an element When a chemical bond forms one of two things happen 1. 2. The number of valence electrons increases to a total of eight All the valence electrons are given up so there are zero Having eight or zero valence electrons makes an element more stable Electron Shells http://en.wikipedia.org/wiki/Atomic_electron_configuration_table Vocabulary Nucleus Proton Neutron Electron Atomic Number Atomic Mass Unit (AMU) Valence electron Electron dot diagram Questions Draw an atom and label each part. What happens to valence electrons during the formation of a chemical bond? Why is the electrical charge of an atom neutral or zero? Why do electrons make up much of an atom’s volume, but not much of its mass?