Introduction to Atoms Notes

Introduction to Atoms: Structure of an Atom ● Atoms are the building blocks of matter and are made of even smaller particles called protons, neutrons, and electrons. Particles in an Atom: ● An atom consists of a nucleus surrounded by one or more electrons. ● The nucleus is the very small center core of an atom. The nucleus is a group of smaller particles called protons and neutrons. ● Protons have a positive electric charge (indicated by a plus symbol, p+). ● Neutrons have no charge. They are neutral. (n) ● The third type of particle in an atom moves in the space outside the nucleus. Electrons move rapidly around the nucleus and have a negative electric charge. An electron is shown by the symbol e-. ● In an atom, the number of protons equals the number of electrons. As a result, the positive charge from the protons equals the negative charge from the electrons. ● Example: Boron has 5p+ and 5e- = no charge A Cloud of Electrons: ● Electrons move around the nucleus, which contains the protons and neutrons. This area is called an electron cloud because electrons may move anywhere within it. Comparing Particle Masses: ● Although electrons occupy most of an atom’s volume, they don’t account for much of its mass. ● A proton and a neutron are about equal in mass. Together, the protons and neutrons make up nearly all the mass of an atom, this is called the Atomic Mass = p + n. (Mass Number) ● Atoms are too small to be measured in everyday units of mass, such as grams or kilograms. Instead, scientists use units known as atomic mass units (amu). ● A proton or a neutron has a mass equal to about one amu. ● The mass of an electron is about 1/2,000 amu. Atoms and Elements ● An element can be identified by the number of protons in the nucleus of its atoms. Atomic Number: ● Every atom of an element has the same number of protons. ● For example, the nucleus of every carbon atom contains 6 protons. Every oxygen atom has 8 protons. ● Each element has a unique atomic number—the number of protons in its nucleus. ● 6 ● C Carbon 12.011 ● Carbon’s atomic number is 6, telling us the number of protons. ● The number of protons is also equal to the number of electrons, so it will have 6 electrons Mass Number (Atomic Mass): ● The mass number is the sum of the protons and neutrons in the nucleus of an atom. (p + n) ● Carbon’s mass number is 12.011 amu ● *Atomic Mass is usually a larger, decimal number. ▪ ▪ 6 ● C Carbon 12.011 Review Questions: 1. What are the 3 main particles in an atom? - proton, neutron, electron 2. How do the particles in an atom differ in electrical charge? - proton = positive charge + - neutron = neutral (no) charge - electron = negative charge 3. Why do atoms have no electrical charge even though most of their particles have charges? - Each atom has equal numbers of positively charge protons and negatively charged electrons. Carbon has +6p and –6e = 0, no charge 4. What is the atomic number of an element? - The number of protons in each atom of that element. 5. How can atomic numbers be used to tell one element from another? - Each element has a unique atomic number because it tells its number of protons. Adding or taking away protons changes the element.