AtomsAtoms

Elements vs. CompoundsElements vs. Compounds

Elements can NOT be chemically broken Elements can NOT be chemically broken down to a simpler substance, compounds down to a simpler substance, compounds can. (Ex. Hcan. (Ex. H22O O H H22 + O + O22))

Pure substances can be either elements Pure substances can be either elements or compounds. Most materials are or compounds. Most materials are MIXTURES of pure substances.MIXTURES of pure substances.

There are only 88 naturally occurring There are only 88 naturally occurring elements, 114 elements that are known.elements, 114 elements that are known.

Dalton’s Atomic TheoryDalton’s Atomic Theory

Elements are made of tiny particles Elements are made of tiny particles called ATOMScalled ATOMS

All atoms of a given element are identicalAll atoms of a given element are identical The atoms of a given element are The atoms of a given element are

different from those of any other elementdifferent from those of any other element

Atomic Theory Cont’dAtomic Theory Cont’d

Atoms of one element can combine with atoms Atoms of one element can combine with atoms of other elements to form compounds. A given of other elements to form compounds. A given compound always has the same relative compound always has the same relative numbers and types of atoms.numbers and types of atoms.

Atoms are indivisible in chemical processes. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply chemical reactions. A chemical reaction simply changes the way atoms are grouped together.changes the way atoms are grouped together.

Law of Constant Law of Constant CompositionComposition

A given compound always contains the A given compound always contains the same proportions (by mass and by same proportions (by mass and by number) of its elementsnumber) of its elements

This means a given compound always This means a given compound always has the same composition, regardless of has the same composition, regardless of where it came from.where it came from.

Chemical FormulasChemical Formulas

A formula describes how a compound is A formula describes how a compound is composed in terms of atoms (how many composed in terms of atoms (how many and which)and which)

How many of each atom are in:How many of each atom are in: NaNa22COCO33

(NH(NH44))33POPO44

ATOMSATOMS

Subatomic ParticlesSubatomic Particles Protons – (pProtons – (p++))

Defines the elementDefines the element Is the integer number (Atomic Number) on the periodic Is the integer number (Atomic Number) on the periodic

tabletable Have a positive chargeHave a positive charge Has a mass of 1 a.m.u.Has a mass of 1 a.m.u.

How many protons does Carbon have?How many protons does Carbon have? How many protons does Iron have?How many protons does Iron have? How many protons does Ununnilium have?How many protons does Ununnilium have? What element has 35 protons?What element has 35 protons?

Subatomic ParticlesSubatomic Particles Neutrons – (nNeutrons – (n00))

Have no (neutral) chargeHave no (neutral) charge Have a mass of ~1 a.m.u.Have a mass of ~1 a.m.u. Contribute to the total mass of an atomContribute to the total mass of an atom Define the Define the isotopeisotope of an atom of an atom

How many neutrons does Carbon-12 have?How many neutrons does Carbon-12 have? How many neutrons does Carbon 14 have?How many neutrons does Carbon 14 have? How many neutrons does Uranium-238 have?How many neutrons does Uranium-238 have?

Subatomic ParticlesSubatomic Particles Electrons – (eElectrons – (e--))

Have a negative chargeHave a negative charge Equal numbers as protons in NEUTRAL atomsEqual numbers as protons in NEUTRAL atoms Gained, lost, or shared in CHEMICAL REACTIONSGained, lost, or shared in CHEMICAL REACTIONS Have a mass of 1/1836 th of a proton (neglible!)Have a mass of 1/1836 th of a proton (neglible!)

How many electrons does Carbon have?How many electrons does Carbon have?

How many electrons does FHow many electrons does F-- have? have?

Make Up Of AtomMake Up Of Atom Protons and Neutrons are in the center of the atom. Protons and Neutrons are in the center of the atom. Electrons are whizzing around on the outside of the Electrons are whizzing around on the outside of the

atom.atom. What element (and isotope) is this atom?What element (and isotope) is this atom?

Empty SpaceEmpty Space

There is a LOT of empty There is a LOT of empty space is in between the space is in between the nucleus and the nucleus and the electronselectrons

If the nucleus was a If the nucleus was a marble on the 50 yard marble on the 50 yard line of a football stadium, line of a football stadium, the electrons would be in the electrons would be in the nosebleed seats…the nosebleed seats…

IsotopesIsotopes Isotopes are atoms of an element that Isotopes are atoms of an element that

have different masses.have different masses. Same element = same # protonsSame element = same # protons Different mass = different # neutronsDifferent mass = different # neutrons

Isotopes are also known as Isotopes are also known as nuclidesnuclides Every element has many nuclides – both Every element has many nuclides – both

stable and unstablestable and unstable The atomic mass on the periodic table is The atomic mass on the periodic table is

the weighted average of all the stable the weighted average of all the stable nuclides of that element.nuclides of that element.

IsotopesIsotopes The specific isotope of any element is written The specific isotope of any element is written

with the generic formulawith the generic formula

ZZAAXX

Where Where Z = the atomic numberZ = the atomic numberA = the mass number (protons + neutrons)A = the mass number (protons + neutrons)X = the elemental symbolX = the elemental symbol

Write the symbol for Magnesium with 13 Write the symbol for Magnesium with 13 neutrons.neutrons.

Chart of NuclidesChart of Nuclides(black = stable, red = (black = stable, red = unstable)unstable)

Chemical v. Nuclear Chemical v. Nuclear ReactionsReactions

Chemical reactions:Chemical reactions: Electrons are involved (exchanged or shared)Electrons are involved (exchanged or shared) Atoms are rearranged, but stay as the same atom.Atoms are rearranged, but stay as the same atom. What we will be studying most this yearWhat we will be studying most this year

Nuclear reactions:Nuclear reactions: Nucleii (protons and neutrons) are involved and Nucleii (protons and neutrons) are involved and

changed.changed. Atoms become different elements by losing or Atoms become different elements by losing or

gaining protons.gaining protons.