Atomic Structure

What is an atom? Atom: the smallest unit of matter that retains the identity of the substance

What is an element? Elements are types of atoms An atom of sodium is different from an atom of sulfur (different identities), but they both are the smallest unit of each substance

Atomic Structure Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Nucleus Electron Cloud

What’s in the Nucleus? The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged particles Neutrons: neutral particles (no charge) Protons and Neutrons make up the mass of the atom

What’s in the Electron Cloud? The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: negatively charged particle with almost no mass The Electron Cloud is most of the atom’s volume

How do the subatomic particles balance each other? When atoms are NEUTRAL…. The # protons = the # electrons If there are 20 protons in an atom then there has to be 20 electrons balance the overall charge of the atom—when the atom is neutral The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

How do we know what’s in an atom? Atomic number = Number of PROTONS Ex: Hydrogen’s atomic number is 1. How many protons does hydrogen have? hydrogen has 1 proton Ex: Carbon’s atomic number is 6. How many protons does carbon have? carbon has 6 protons **The number of protons identifies the atom. Which element has 2 protons? Which element has 29 protons?

How do we know what’s in an atom? Mass number: the number of protons and neutrons in the nucleus (electrons are so small they’re not counted) Ex: hydrogen can have a mass of 3. Since it has 1 proton it must have 2 neutrons # of neutrons = mass # - atomic #

What’s the units?

Determining the number of protons and neutrons Li has a mass number of 7 and an atomic number of 3 How many Protons? = 3 How many Neutrons? 7-3 = 4 (mass # - atomic #) Ne has a mass number of 20 and an atomic number of 10 How many Protons? = 10 How many Neutrons? = 20 - 10= 10

Why are mass numbers on my table not whole numbers? ISOTOPES: atoms with the same atomic number but different # neutrons. This doesn’t affect the identity This doesn’t affect the charge This gives the atom a different mass number The periodic table mass numbers are averages Round to the nearest whole number to do calculations

What about the electrons? To be neutral the # electrons must be equal to the # protons So e- = p+ = atomic # Ex: He has a mass # of 4 and an atomic # of 2 p+ = 2 no = 2 e- = 2

Determine the number of subatomic particles in the following: Cl has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17 K has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20, e- = 19

Preview: How exactly are the particles arranged? Bohr Model of the atom: Nucleus: all of the protons and the neutrons The 3rd ring can hold up to 8 e- The 1st ring can hold up to 2 e- The 4th and 5th rings can hold up to 16 e- The 2nd ring can hold up to 8 e-

What does carbon look like? Mass # = 12 atomic # = 6 p+ = 6 no = 6 e- = 6 6 p and 6 n live in the nucleus

Color code your periodic table Make sure you draw a dark line to separate metals from nonmetals Noble Gases