general’science’101’csma31.csm.jmu.edu/physics/nikolic/lectures/gsci101/11chemistry.pdf ·...

General Science 101

The atomic nature of Ma5er

Chapters 11 and 32

GSCI 101, Prof. M. Nikolic 2

•  First developed concept of atom

•  Atom is the smallest parEcle that could not be divided any further

Democritus and Leuccipus (5th century BCE)

The Atomic hypothesis

Aristotle (350 BCE)

•  All ma5er is composed of combinaEons of 4 elements – Earth (solids)

– air (gas) – water (liquids)

– fire (state of flame)

•  Persisted for more than 2000 years

The discovery of atom


John Dalton (1766 -‐ 1844)

•  Set foundaEons of modern chemistry by proposing his atomic theory

1) All ma5er is made of atoms. Atoms are indivisible and indestrucEble.

2) All atoms of a given element are idenEcal in mass and properEes.

3) Compounds are formed by a combinaEon of two or more different kinds of atoms.

4) A chemical reacEon is a rearrangement of atoms.

•  No proof

Basics of Dalton’s theory are sEll valid.


•  Sco]sh botanist

•  Observed that grains of pollen placed into a clear liquid moved strangely as if pushed with invisible parEcles – Brownian mo*on

•  The first detecEon of atoms

Robert Brown (1773 – 1858)

The discovery of atom

Albert Einstein (1879 – 1955)

•  1905 – explained Brownian moEon and confirmed the existence of atoms

•  Also got Nobel prize for this

Atomic structure


Brown – All ma5er is made of atoms. Atoms are indivisible and indestrucEble.

Atomic structure

•  Atomic nucleus – filled with nucleons •  Protons – posiEvely charged

nucleons •  Neutrons – neutral nucleons

•  Electron shell – negaEvely charged

Discovery of atomic nucleus

GSCI 101, Prof. M. Nikolic 6 Same charges repel and opposite charges a5ract each other.

Ernest Rutherford (1907)

Atom – small, massive and posiEvely charged core (nucleus) – large shell filled with light electrons

Discovery of the electrons


Joseph John Thomson (1897)

Chapter 32 – The atom and quantum

Conceptual quesEon: Atomic structure

Proton.

Neutron.

Electron.

Except for slight differences, all have about the same mass.

Need more informaEon

Which of the following has the smallest mass?


✓

The elements


Substance composed of only one kind of atom is called an element.

ScienEsts discovered 117 different kinds of elements

– 90 occur in nature. – Others produced in laboratory are unstable.

The Elements

99.9 % of Earth is formed from a dozen of the elements

ComposiEon of living things include these 5 elements: •  Oxygen (O) •  Carbon (C) •  Hydrogen (H) •  Nitrogen (N) •  Calcium (Ca)

10 GSCI 101, Prof. M. Nikolic

Atomic structure


ProperEes of elements and atoms 1.   Atomic number (Z) – number of protons in the nucleus of an atom

– neutral atom: number of protons = number of electrons – all atoms in elements have the same Z

Example: Hydrogen (H)

Z = 1 → 1 proton Neutral hydrogen → 1 electron

Atomic structure


ProperEes of elements and atoms 2. Mass number (A) – total number of protons and neutrons together

Example: Hydrogen (H)

Z = 1 → 1 proton Neutral hydrogen → 1 electron

A = 1 → 0 neutrons

Example: Lithium (Li)

Z = 3 → 3 protons Neutral Li → 3 electrons

A = 7 → 4 neutrons

Isotopes


Atoms of the same element that have different numbers of neutrons are called isotopes.

We idenEfy isotopes by their mass number A.

Three isotopes of Carbon

Atomic structure


ProperEes of elements and atoms 2.   Atomic mass (A) – total mass of an atom

a)  Electrons – small mass → negligible contribuEon b)  Protons c)  Neutrons

Atoms have so small mass that it is hard to express their mass in grams and kilograms → atomic mass unit (amu) -‐ 1nucleon (proton or neutron) → mass of 1 amu

Atomic mass unit is defined as 1/12 of the mass of a carbon-‐12 (12C)


Protons in the nucleus of an atom.

Electrons in a neutral atom.

All of the above.

None of the above.

The atomic number of an element matches the number of


✓


44 neutrons.

56 neutrons.

100 neutrons.

None of the above.

A nucleus with an atomic number of 44 and a mass number of 100 must have


✓

Z = 44 → 44 protons A = 100 → 100 – 44 = 56 neutrons

Electron configuraEon


Niels Bohr (1885 – 1962)

•  Postulated the idea of atomic structure based on Rutherford’s experiments

•  Electrons populate shells with specific energies around nucleus

1.  Electrons in the same shell have the same energy.

2.  Electrons can only jump between shells.

Why don’t electrons fall onto the nucleus?


Electrons are not just parEcles, they are waves too!

Even more, they standing waves è These waves close in on themselves.

Not an orbit for an electron.

Electron’s mass and charge are spread out over the wave.

Even the smallest orbit of electrons sEll has to close on itself è Electrons cannot fall, they have to circle.



Electrons are not just parEcles, they are waves too!



Modern quantum mechanics – electron wave is spread out in 3 dimensions forming an electron “cloud” of probability.

We can only calculate the probability of finding the electron in the cloud (Schrodinger’s wave equa3on).

Why?

Because of the Heisenberg uncertainty principle. We ether know where the electron is or how fast it is.



Niels Bohr (1885 – 1962)

•  Postulated the idea of atomic structure based on Rutherford’s experiments

•  Electrons populate shells with specific energies around nucleus

1.  Electrons in the same shell have the same energy.

2.  Electrons can only jump between shells.



The arrangement of electrons in shells is called electron configura*on.

Elements may have up to 7 shells also called energy levels

a)  n = 1, shell K b)  n = 2, shell L c)  n = 3, shell M, …

Each shell may have up to 4 subshells also called orbitals

a)  s = 2 electrons b)  p = 8 c)  d = 10 d)  f = 14



Number of orbitals in a shell ≤ n (number of the shell).

a)  n = 1, only s orbital and up to 2 electrons → 1s2

b)  n = 2, s and p orbitals → 2s2 2p6

c)  n = 3, s, p, and d orbitals → 3s2 3p6 3d10

d) n = 4, s, p, d, and f orbitals → 4s2 4p6 4d10 4f14

e) n = 5, s, p, d, and f orbitals → 5s2 5p6 5d10 5f14

Example: Chlorine 17Cl Z = 17 → 17 protons → 17 electrons

n =1 → 1s2 (2 electrons) n = 2 → 2s2 2p6 (8 electrons) n = 3 → 3s2 3p5 (7 electrons)

Electron configuraEon -‐ rules


Exercise : Find the electron configuraEon copper 29Cu Z = 29 → 29 electrons

1s2 2s2 2p6 3s2 3p6 4s2 3d9

n = 1 → 1s2 (2 electrons) n = 2 → 2s2 2p6 (8 electrons) n = 3 → 3s2 3p6 (8 electrons) – total of 18 electrons n = 4 → 4s2 (2 electrons) – total of 20 electrons n = 3 → 3d9

4s orbital comes before 3d orbital!

Before going to 3d orbital check what happens with 4s

Periodic table of elements


Periodic table of the elements


a)  Elements are classified by their atomic number (Z)

b)  Groups A – representaEve elements B – transiEon elements

Periods – how many shells (n) are there in an atom

Group A – how many electrons are in the last shell

Periodic table of the elements


Group A a)  I A – 1 electron – alkali metals

(shiny, sot metals)

b)  II A – 2 electrons – alkaline earth metals

c)  VII A – 7 electrons – halogens (very reacEve)

d)  VIII A – 8 electrons – filled outer shell – inert gases (colorless, odorless, nonreacEve gases)

Exercise: Periodic pracEce


Write down the electron configuraEon of silicon (14Si) and then idenEfy its period and group. Silicone 14Si Z = 14 → 14 protons → 14 electrons

n =1 → 1s2 (2 electrons) n = 2 → 2s2 2p6 (8 electrons) n = 3 → 3s2 3p2 (4 electrons)

Silicon belongs to 3rd period, IV A group

What about iron (26Fe)? Iron 26Fe Z = 26 → 26 protons → 26 electrons

n =1 → 1s2 (2 electrons) n = 2 → 2s2 2p6 (8 electrons) n = 3 → 3s2 3p6 (8 electrons) n = 4 → 4s2 (2 electrons) -‐ total of 20 electrons n = 3 → 3d6

Iron belongs to 4rd period, VIII B group (you add up 2e-‐from 4s and 6e-‐ from 3d)

Ions and neutrals


Neutral atom è number of protons = number of electrons

If an atom loses/gains a proton è it becomes a different atom (element). If an atom loses/gains a neutron è it becomes a different isotope of the same element.

Compounds and mixtures


When atoms of different elements bond to one another, they make a compound.

– A compound is different from the elements from which it is made. – It can only be separated into its consEtuent elements by chemical means. Example: Salt (a compound of sodium and chlorine)

A substance that is mixed together without chemically bonding is

called a mixture.

Example: Air (a mixture of several gases)

Molecules Molecules •  Two or more atoms bonded together Example: •  NH3 (ammonia) •  3 atoms of hydrogen and 1 atom of nitrogen

Why do atoms bond into molecules? GSCI 101, Prof. M. Nikolic 31

Valence electrons


Electrons populaEng the last electron shell are called valence electrons.

•  Groups in the periodic table contain an informaEon on how many valence electrons each element has. •  VIII A group – 8 electrons filled shell – most stable elements

Carbon 6C Z = 6 → 6 electrons

n =1 → 1s2 (2 electrons) n = 2 → 2s2 2p2 (4 electrons)

Octet rule – atoms a5empt to acquire an outer shell with 8 electrons.

Halogen elements


Group VII A – 7 valence electrons

Fluorine 9F Z = 9 → 9 electrons


Fluorine is one electron short of having a completely full 2p orbital.

•  To saEsfy the octet rule and have stable configuraEon with 8 valence electrons, fluorine is pracEcally begging to gain 1 electron

•  On the other hand, fluorine (and the other halogens) isn’t too keen on accepEng any more than one electron.

Other elements


Group VI A – 6 valence electrons Oxygen 8O Z = 8 → 8 electrons


Oxygen has two vacancies in the last shell.

Group V A – 5 valence electrons Nitrogen 7N Z = 7 → 7 electrons


Nitrogen has three vacancies in the last shell.

On the other side of periodic table


Group I A – 1 valence electron

Sodium 11Na Z = 11 → 11 electrons

n =1 → 1s2 (2 electrons) n = 2 → 2s2 2p6 (8 electrons) n = 3 → 2s1 (1 electron)

Only one electron. If sodium gets rid of that electron, then the configuraEon of the remaining electrons is very stable.


Metals These elements are trying to lose an electron, or two.

Non-‐metals These elements are trying to gain an electron, or two (even three).

We are not going to discuss these, they are too complicated.

Ionic bonds


In an ionic bond, a metal gives up one or more electrons and a non-‐metal accepts one or more electrons.

What happens when a sodium atom meets a chlorine atom?

Na

loses electron è posiEve ion

Cl

gains electron è negaEve ion

The oppositely charged ions stay bound together, forming the molecule NaCl (table salt)

Ionic bonds


What happens if magnesium meets up with chlorine?

Cl Cl

One of magnesium’s extra electrons goes to a chlorine atom, but that chlorine atom won’t accept more.

So another chlorine atom appears and takes the other electron magnesium wants to give up. In this molecule, for every one magnesium we have two chlorines: MgCl2.

Mg

Covalent bonds


A covalent bond is a chemical bond formed by the SHARING of at least a pair of electrons.

•  Each of these fluorine atoms is willing to share one electron with the other.

•  Each fluorine atom is then fooled into thinking it has the same configuraEon as neon. The resulEng molecule is F2.

Covalent bonds


•  Similar processes occur to form H2, Cl2, Br2 and I2.

•  What about oxygen?

•  Each atom of oxygen is willing to share two electrons.

•  Each oxygen shares two of its electrons with another oxygen.

•  Each oxygen atom is then fooled into thinking it has the same configuraEon as neon. The resulEng molecule is O2.

Covalent bonds


Naturally, non-‐metal atoms can join up with non-‐metal atoms of other elements in covalent bonds.

The red circles, represenEng the electrons, are ge]ng shared •  Each hydrogen atom “has” 2

electrons

•  Oxygen atom “has” 8 electrons

Molar mass


Molar mass of a molecule is the sum of the atomic masses (amu) of all the atoms in a molecule.

Exercise : What is the molar mass of water, which has the formula H2O?

Atoms Atomic mass unit (amu)

2 of H 2 x 1 amu = 2 amu

1 of O 1 X 16 amu = 16 amu

Molar mass (M) = 18 amu

Exercise: Molar mass


What is the molar mass of ethyl alcohol, which has the formula C2H5OH?

Atoms Atomic mass unit (amu)

2 of C 2 x 12 amu = 24 amu

6 of H 6 x 1 amu = 6 amu

1 of O 1 X 16 amu = 16 amu

Molar mass (M)

= 46 amu

Units of measurement


Atomic mass unit (amu) is based on 12 g of isotope Carbon-‐12.

In 12 g of Carbon-‐12 there is 6.0 x 1023 atoms è Avogadro’s number (Na)

The amount of substance that contains Avogadro’s number of parEcles is defined as a MOLE of the substance.

1 mole è Na = 6.0 x 1023 parEcles è 12 g of Carbon-‐12

What about other elements?

Hydrogen: 1 mole è 6.0 x 1023 parEcles è 1 g of Hydrogen-‐1 Oxygen: 1 mole è 6.0 x 1023 parEcles è 16 g of Hydrogen-‐16 Magnesium: 1 mole è 6.0 x 1023 parEcles è 24 g of Magnesium-‐24

Conceptual quesEon: Mole and Avogadro’s number

1.

10.

6.0x1023

15x6.02x1023

31x6.02x1023

How many atoms is in 1 mole of Phosphorus (P)?


✓

One mole of any element is always 6.0 x 1023 atoms.

Three moles of any element are always 3 x 6.0 x 1023 atoms = 18 x 1023 atoms, etc.

NotaEon for mole is: n (small le5er n).

Or, by applying mathemaEcal formula:

N = n ⋅Na N – number of parEcles n – number of moles Na – Avogadro’s number

Mass of elements and molecules


Mass of an element/molecule is given with the formula:

m = n ⋅M m – mass of the molecule given in grams n – number of moles M – molar mass given in amu

Example: What is the mass of 2 moles of water?

First, find the molar mass of the water M(H2O): M(H2O) = 2xA(H) + 1xA(O)

= 2x1 + 1x16 = 18 amu

Then, find the mass using the formula: m(H2O) = n x M(H2O)

= 2 moles x 18 amu = 36 g

If we are looking for the mass of an element than use atomic mass of the element.

Conceptual quesEon: Mole and Avogadro’s number

36 amu.

36 g.

72 amu.

72 g.

Need more info.

What is the mass of 2 moles of Chlorine atom?


✓

What about chlorine molecule Cl2?

The same rules apply for molecules just instead of atomic mass unit you should use molar mass (M).

Atomic mass of chlorine A(Cl) = 36 amu

m(Cl) = n x A(Cl) = 2 moles x 36 amu = 72 g

The molar mass: M(Cl2) = 2 x A(Cl) = 2x36 = 72 amu

m(Cl2) = n x M(Cl2) = 2 moles x 72 amu = 144 g

Exercise: Mole and mass I


What is the mass of 4 moles of iron oxide, Fe2O3?

m = n x M(Fe2O3)

First, find the molar mass of the iron oxide M(Fe2O3):

M(Fe2O3) = 2xA(Fe) + 3xA(O) = 2x56 + 3x16 = 112 + 48 = 160 amu

m = 4 moles x M(F2O3) = 4 moles x 160 amu = 640 g = 0.64 kg

Exercise: Mole and mass II


How many atoms are in 96 g of O2?

To find number of atoms we need number of moles in O2

Since:

m = n x M(O2)

If we find molar mass of O2 we could solve for number of moles.

Molar mass of O2: M(O2) = 2xA(O) = 2x16 = 32 amu

Number of moles of O2: 96 g= n x 32 amu è n = 96/32 = 3 moles

Number of atoms of O2: N = n x Na N = 3 moles x 6x1023 = 18x1023 atoms

AnEma5er


Ma5er è Composed of atoms with posiEve nuclei and nega3ve electrons

An*maYer è Composed of atoms with nega*ve nuclei and posi%ve electrons (positrons)

AnEma5er


•  Positron was discovered in 1932 •  The first arEficial anE-‐atom was constructed in 1995

Every charged parEcle has an anEparEcle of the same mass and opposite charge.

Even neutrons have anE-‐neutrons.

AnEma5er


•  GravitaEonal force does not disEnguish between ma5er and anEma5er •  Both ma5er and anEma5er emit the same light

There could be galaxies made of anEma5er and we would not know!

But when anEma5er meets the ma5er they mutually annihilate each other converEng the equal amounts of ma5er and anEma5er

to energy (E=mc2)

Conceptual quesEon: AnEma5er

1 gram.

2 grams.

4 grams.

Much more than 4 grams.

If 1.0 gram of anEma5er meets with 4.0 grams of ma5er, the energy released would correspond to the energy equivalent of


✓

When ma5er meets the anEma5er they annihilate the equal amounts of masses. Since we have only 1 gram of anEma5er è this is the most mass that anEma5er can annihilate

+ The same amount of mass from the ma5er (1 g) è Total energy released corresponds to the

energy equivalent of 1 g + 1 g = 2 g

Dark ma5er


Dark ma5er is NOT an anEma5er!

Dark ma5er is the strange and unknown ma5er that cannot be seen, since it does not reflect, absorb or emit light.

ScienEsts predicted dark ma5er because gravity laws were not adding up for most of the galaxies in our universe.

Dark energy is the property of space – it counterparts the gravity and causes the universe to expand.

general’science’101’csma31.csm.jmu.edu/physics/nikolic/lectures/gsci101/11chemistry.pdf ·...

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