1. Structure of an Atom

2. What Is an Atom? An atom is often referred to as the building block of matter. Atoms have a nucleus surrounded by an electron cloud subatomic proton neutronelectron Atoms are composed of smaller subatomic particles in an atom. The proton, neutron, and electron. element Each element is composed of one type of atom and can not be broken down into a simpler substance

3. Inner Structure of an Atom Nucleus - Small, dense, positively charged center of the atom which contains most of the atom’s mass The nucleus contains subatomic particles that have certain characteristics:  Protons (  Protons (p+) - positively charged particles in the nucleus of the atom, contribute to the atom’s mass  Neutrons  Neutrons (n o )- particles in the nucleus that have no charge, but contribute to the atom’s mass NEUTRAL

4. Outer Structure of an Atom ● Electron cloud ● Electron cloud - an area encircling the nucleus where electrons are likely to be found energy levels ● The cloud contains energy levels  electrons (  electrons (e - )are negatively charged particles located in specific energy levels  energy levels completely surround the nucleus  there is a specific order for the electrons to fill the energy levels

5. Outer Structure of an Atom ● Energy levels ● Energy levels completely surround the nucleus Maximum of 2 electrons Nucleus Maximum of 8 electrons Maximum of 18 electrons Maximum of 32 electrons Maximum of 50 electrons

6. Outer Structure of an Atom ● valence electrons ● valence electrons are in the outermost energy level and are the electrons involved in bonding  valence electrons determine the number of bonds an atom can form  an atom is most stable when its outermost energy level is full

7. Atom Characteristics atomic number The number of protons in the nucleus is the atomic number of that atom. The number of protons (+) equals the number of electrons (-) in a neutral atom mass number The mass number is the mass of the protons plus the mass of the neutrons atomic mass units amu  mass is reported in the SI units atomic mass units (amu)  Protons and neutrons each are given an amu of 1  Electrons have a mass of nearly zero

8. Decoding Atom Information C carbon 6 12.011 Symbol Name # of protons Atomic mass

9. Decoding Atom Information: carbon 12.011 # of protons = # of electrons in a neutral atom Atomic mass is a weighted average of all the isotopes of an element 6 C

10. The mass number of an atom is for a particular isotope of that element Mass number is the total number of protons and neutrons in the nucleus Example for C-12: ◦ 6 protons + 6 neutrons= 12 ◦ 12 is the mass number for Carbon-12 *13 is the mass number for Carbon-13 and comes from C-13 having 6 protons and 7 neutrons