The Atom: Structure

Inside the Atom Electrons Protons Neutrons Nucleus Beryllium Atom

Nucleus -small, dense, overall positive charge -located at center of atom -contains most of atom's mass -contains protons & neutrons -very dense

Protons -same size and mass - used to set the unit for mass of subatomic particles atomic mass unit (amu) -called the atomic mass unit (amu) ; 1 proton = 1 amu -charge: positive -mass: 1 amu -location: nucleus proton +

Neutrons -all identical -slightly larger than protons (not enough to matter) -charge: none (neutral) -mass: 1 amu -location: nucleus neutron

Electrons -smaller than protons -equal and opposite in charge -size of electron clouds determines the size of the atom -charge: negative -mass: zero -location: electron clouds outside the nucleus electron -

Ions -atoms are neutral (no overall charge) -due to equal but opposite charge of protons & electrons -protons & electrons are equal in number, so their charges cancel out -if number of protons & electrons becomes ion unequal, atom becomes and ion -number of protons > number of electrons = positive charge -number of protons < number of electrons= negative charge H+H+ 1 proton, no electrons Positive charge H 1 proton, 1 electron No charge H-H- 1 proton, 2 electrons Negative charge

Differences in Atoms -each element has a different number of protons, neutrons, & electrons -the more it has, the larger it is EX: -Hydrogen: 1 proton, 1electron, 0 neutrons -Helium: 2 protons, 2 neutrons (help hold the nucleus together), 2 electrons Hydrogen Helium

Telling them Apart atomic -the number of protons in an atom is its atomicnumber -determines what element an atom represents -all atoms of an element have the same atomic number EXAMPLE: Oxygen has 8 protons, so its atomic number is 8. Atomic Number

Same Element, Different Atom isotope -isotope – atoms (of the same element) with the same number of protons, but a different number of neutrons -EX: A) add a neutron to a hydrogen atom B) mass now different, but atomic number still 1 isotope C) still hydrogen, but different isotope HydrogenHydrogen-2

Properties of Isotopes -each element has a limited number of naturally occurring isotopes -isotopes of an element share most physical & chemical properties -some isotopes unstable & therefore radioactive mass number -isotopes of an element identified by mass number mass number -mass number = protons + neutrons -named by writing: element name-mass number EXAMPLE: Hydrogen with a mass number of 2: Hydrogen-2 Boron with a mass number 10: Boron-10

Mass of Elements -most elements contain two or more isotopes EX: All Copper (Cu) is made of Copper-63 and Copper-65 atoms atomic mass -atomic mass is a weighted average of each isotope present (a weighted average goes by the percent of each isotope) EX: Copper is 69% copper-63 & 31% copper-65

Forces in the Atom -4 basic forces at work in the atom: 1) Gravity - force of attraction that pulls objects toward each other. Depends on mass of the objects and distance between them. Force of gravity in the atom is very small. 2) Electromagnetic Force - causes like charges to repel and opposite charges to attract. Holds electrons in place around the nucleus. 3) Strong Force - helps hold the nucleus together At close distances is stronger than the electromagnetic force. 4) Weak Force – helps convert neutrons into protons or electrons in unstable (radioactive) atoms.