AtomsUnit 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 (n0), & 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 [n0] – non-charged subatomic particle [neutral]– found in the nucleus of an atom

– relative mass = slightly larger than 1 amu

– new theories: [p+] + [e-] = [n0] ?

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 1/1936th of 1 amu…]

• Quarks?– theoretically = smaller particles that

make up (p+), (n0), & (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?

ElementsElements 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 SymbolMass 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 NECESSARYNOT ALL OF THESE ARE NECESSARY

Ag108

47

+4

Counting Particles

• p+s = Atomic Number

• n0s = Atomic Mass – Atomic Number

• e-s = p+s Cl35

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 n0s 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: [O2], Ozone [O3]

Allotropes of Carbon

a. diamondb. graphitec. lonsdaleited. buckyballs [C60 –

buckminsterfullerene]e. C540f. C70g. “amorphous” carbon

[not truly amorphous]h. single-walled

carbon nanotube / buckytube

Allotropes of Oxygen

Electron-Dot Models

• p+s & n0s 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 ofelements, 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

PracticeThe total number of nucleons is

atomic mass, atomic number, nucleon count, state of matter

Atoms of an element with different number of neutrons areallotropes, 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?