Previously we learned that the average human body has 10,000,000,000,000 (10 Trillion) cells Q: How many atoms are in one cell?

A: 200,000,000,000, x more than there are stars in the milky way 2,000,000,000,000,000,000,000, septillion atoms in the body

 Crash Course History of Atomic Structure Crash Course History of Atomic Structure

The term matter describes all of the physical substances around us: your table, your body, a pencil, water, and so forth

 Anything that has mass and takes up space (has volume)  Made up of different kinds of atoms

 Includes all things that can be seen, tasted, smelled, or touched  Does not include heat, sound, or light

Models are often used for things that are too small or too large to be observed or that are too difficult to be understood easily

 In the case of atoms, scientists use large models to explain something that is very small  Models of the atom were used to explain data or facts that were gathered experimentally.  So, these models are also theories

 Universe was made of empty space and tiny bits of stuff  Called these tiny bits of stuff atomos  Atomos could not be divided

 All elements are composed of indivisible particles (atoms).  Atoms of the same element are the same  Atoms of different elements are different.  Compounds consisted of atoms of different elements combined together

 Mostly empty space  Small, positive nucleus  Contained protons  Negative electrons scattered around the outside

 Used an electric current to learn more about atoms  Noticed “electrons” were attracted to a positive end

 Sometimes called the wave model  Spherical cloud of varying density  Varying density shows where an electron is more or less likely to be

 Nucleus ◦ Protons ◦ Neutrons  Electrons

 Tiny, very light particles  Have a negative electrical charge (-)  Move around the outside of the nucleus

 Protons  Much larger and heavier than electrons  Protons have a positive charge (+)  Located in the nucleus of the atom

 Neutrons  Large and heavy like protons  Neutrons have no electrical charge  Located in the nucleus of the atom

 Atomic Number = number of protons  In a neutral atom, the # of protons = the # of electrons

 Atomic Mass Number - equal to the number of protons plus neutrons.

 Atomic Number: number of protons in an element ◦ Zr=40 protons…and _______electrons  Mass Number: Protons + neutrons ◦ H= 1 mass # ◦ He=4 mass #