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
-called the atomic mass unit (amu) 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 determinesthe 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 unequal, atom becomes and ionion-number of protons > number of electrons = positive charge-number of protons < number of electrons= negative charge
H+
1 proton, no electronsPositive charge
H1 proton, 1 electronNo charge
H-
1 proton, 2 electronsNegative charge
Differences in Atoms-each element has a different number of protons, neutrons, & electrons-the more it has, the larger it isEX:-Hydrogen: 1 proton, 1electron, 0 neutrons-Helium: 2 protons, 2 neutrons (help hold the nucleus together), 2 electrons
HydrogenHelium
Telling them Apart-the number of protons in an atom is its atomic atomic numbernumber
-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-isotopeisotope – atoms (of the same element) with the samenumber of protons, but a different number of neutrons
-EX:A) add a neutron to a hydrogen atomB) mass now different, but atomic number still 1C) still hydrogen, but different isotopeisotope
Hydrogen Hydrogen-2
Properties of Isotopes-each element has a limited number of naturallyoccurring isotopes-isotopes of an element share most physical & chemical properties-some isotopes unstable & therefore radioactive-isotopes of an element identified by mass numbermass number -mass numbermass 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 anddistance 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.
