Atoms Unit 2 – Lecture 3 Building Blocks of Matter

Atoms smallest particle of an element that retains its chemical properties composed of subatomic particles –protons (p + ), neutrons (n 0 ), & electrons (e - ) –“sub-” = below, less than

Subatomic Particles Types of Subatomic Particles Protons [p + ] – positively charged subatomic particle –found in the nucleus of an atom –relative mass = 1 amu [atomic mass unit] Neutrons [n 0 ] – non-charged subatomic particle [neutral] –found in the nucleus of an atom –relative mass = slightly larger than 1 amu –new theories: [p + ] + [e - ] = [n 0 ] ?

Subatomic Particles – cont’d Electrons [e - ] – negatively charged subatomic particle –found outside of the nucleus in energy levels [aka e - clouds, e - shells, etc] –no relative mass [actual mass is 1/1936 th of 1 amu…] Quarks? –theoretically = smaller particles that make up (p + ), (n 0 ), & (e - ) –have their own branch of “theoretical physics”

Practice Which subatomic particle is neutral? Which describes a single particle of an element? Which subatomic particle is negative? Which subatomic particle may or may not exist? Which is a single particle of a compound? Which subatomic particle is positive?

Elements Elements are made of atoms. atomic number – number of e - or p + chemical symbol – name of element atomic mass – number of “nucleons” nucleon = particle in the nucleus

Elements – cont’d Elements are found on the periodic table in their natural, neutral state –meaning, they’re neutral = same # of p + & e -

Practice - Oxygen atomic mass? number of protons? atomic number? number of electrons? chemical symbol? number of neutrons?

More Practice An atom with 4 protons and 6 neutrons would: –have a mass of…? –have an atomic number of…? –have … electrons typically? –be which element?

Writing Elements - Silver Write: Chemical Symbol Mass Number at the upper-left of the symbol Atomic Number at the lower-left of the symbol Charge [if applicable] at the upper-right hand corner NOT ALL OF THESE ARE NECESSARY Ag

Counting Particles p + s = Atomic Number n 0 s = Atomic Mass – Atomic Number e - s = p + s Cl 35 17

Counting Particles – cont’d if e - s differ –called ion charge is different –more e - s [than normal] = more negative charge –less e - s [than normal] = more positive charge

Counting Particles – cont’d if n 0 s differ –called isotope “iso-” = equal/same –same chem & phys properties –atomic mass on periodic table is average of isotopes if p + s differ –is a different element

Isotopes – Examples

Different Atoms, Same Element Allotrope – different natural/physical forms of an element “allo-” = other/different Ex. for Carbon: Graphite, Diamond, Buckminsterfullerenes [buckyballs]… Ex. for Oxygen: [O 2 ], Ozone [O 3 ]

Allotropes of Carbon a.diamond b.graphite c.lonsdaleite d.buckyballs [C60 – buckminsterfullerene] e.C540 f.C70 g.“amorphous” carbon [not truly amorphous] h.single-walled carbon nanotube / buckytube

Allotropes of Oxygen

Electron-Dot Models p + s & n 0 s exist in the nucleus e - s exist in electron/energy shells around the nucleus –“octet rule” - atoms will gain, lose, or share e - s to become chemically stable [8 e - s in valence shell] valence shell = outer-most shell –e - s in valence shell = valence e - s

Electron-Dot Models Draw Nucleus Protons Neutrons

Electron-Dot Models – cont’d Draw Electrons Electron Levels *2* 8…

Practice Atoms are the smallest particle of elements, compounds, homogeneous mixtures, heterogeneous mixtures Which subatomic particle has a neutral charge? protons, neutrons, electrons, quarks What is the dense center of an atom called? protium, nucleus, neutron core, core

Practice Which property discerns atoms from one another? atomic mass, mass number, atomic number, none of the above Which property discerns atoms from one another? atomic mass, mass number, atomic number, none of the above Atomic Number is based on which property of atoms? # of protons, # of electrons, # of neutrons, total # of particles

Practice The total number of nucleons is atomic mass, atomic number, nucleon count, state of matter Atoms of an element with different number of neutrons are allotropes, isotopes, megatopes, gigatropes Which subatomic particles are not included in calculating Atomic Mass? protons, neutrons, electrons, nucleons

Practice How many neutrons are in Oxygen-16, which has an atomic number of 8? 4, 6, 8, 10, 12, 14, 16 How many neutrons are in Oxygen-18, which has an atomic number of 8? 4, 6, 8, 10, 12, 14, 16 Which subatomic particle has a positive charge? Protons, Neutrons, Electrons, Quarks How many e - s fit in an atom’s first electron level?