chapter 5 atomic structure. what are atoms made of? atoms are made of small particles called...

21
Chapter 5 Chapter 5 Atomic Structure Atomic Structure

Upload: nathaniel-romero

Post on 10-Dec-2015

230 views

Category:

Documents


0 download

TRANSCRIPT

Chapter 5Chapter 5Atomic StructureAtomic Structure

What are atoms made of?What are atoms made of?

Atoms are made of small particles Atoms are made of small particles called called protons, electrons, protons, electrons, neutronsneutrons..

These particles are called These particles are called sub-sub-atomic particlesatomic particles

Where in the atoms are these Where in the atoms are these sub-atomic particles found?sub-atomic particles found?

E

Electron circle the atoms in areas called shells

Protons and neutrons are known as nucleons

Protons and neutrons are Found in the nucleus

Structure of an Atom - Structure of an Atom - ElectronElectron

E

Found in shells which surround the atom

Carries a charge of -1

Has negligible mass or Relative mass of 1 / 1840.

Represented by symbol, e

Structure of an Atom - Structure of an Atom - NeutronNeutron

E

Found in nucleus which Is in the centre of an atom.

Carries no charge (Charge = 0)

Relative mass of -1

Represented by symbol, n

Structure of an Atom - Structure of an Atom - ProtonProton

E

Found in nucleus which Is in the centre of an atom.

Carries a charge of +1

Relative mass of 1

Represented by symbol, p

The proton and nucleon The proton and nucleon numbernumber

All atoms are All atoms are electrically neutralelectrically neutral An atoms contains An atoms contains an equal an equal

number of positively charged number of positively charged protons and negatively changed protons and negatively changed neutronsneutrons

Number of Protons = Number of Number of Protons = Number of NeutronsNeutrons

Therefore, number of Therefore, number of positive positive chargescharges = number of = number of negative negative charge charge Electrically neutral Electrically neutral

The proton and nucleon The proton and nucleon numbernumber

Number of protons in an atom is Number of protons in an atom is called the proton numbercalled the proton number

It is also known as atomic numberIt is also known as atomic number Proton number is represented by Proton number is represented by

symbol symbol ZZ Proton number can also tell us Proton number can also tell us

number of electrons in atom.number of electrons in atom.

The proton and nucleon The proton and nucleon numbernumber

An Example:An Example:

For example, the proton number of For example, the proton number of nitrogen is 7. Hence we can nitrogen is 7. Hence we can deduce that a nitrogen atom has deduce that a nitrogen atom has 7 7 protons and 7 nucleons protons and 7 nucleons

Different atoms have Different atoms have different proton numbersdifferent proton numbers

Each element has a Each element has a unique unique proton numberproton number

Atoms of Atoms of different elementsdifferent elements have have different number of protonsdifferent number of protons

Oxygen, for example, has Oxygen, for example, has a proton a proton number of 8number of 8

Any atom with 8 protons Any atom with 8 protons must be must be an oxygen atom.an oxygen atom.

Nucleon Number (mass Nucleon Number (mass number)number)

Nucleon number is the Nucleon number is the total number total number of protons and nucleons in an atomof protons and nucleons in an atom

It is represented by letter It is represented by letter AA Nucleon number (A) = number of Nucleon number (A) = number of

protons + Number of neutronsprotons + Number of neutrons The nucleon number is also called The nucleon number is also called mass mass

numbernumber This is because This is because the mass of an atom the mass of an atom

depends on number of protons and depends on number of protons and neutrons in an atom.neutrons in an atom.

Representing proton and Representing proton and nucleon numbernucleon number

The The nucleonnucleon and and proton number can proton number can be includedbe included when representing an when representing an element in symbols.element in symbols.

An element is An element is represented using only represented using only the nucleon number (Example: the nucleon number (Example: sodium23 or 23-Na)sodium23 or 23-Na)

23

11Na

Nucleon number is superscript, top-left of the symbol

Proton number is subscript, bottom-left of symbol

ChemicalSymbol

Isotopes: Hydrogen AtomsIsotopes: Hydrogen Atoms

E E E

How are they different from the first one?These hydrogen atoms are known as isotopes. Notice that these atomshave the same number of protons but different number of neutrons

IsotopesIsotopes

Isotopes Isotopes are atoms of the same are atoms of the same element (with same number of element (with same number of protons) but different number of protons) but different number of neutronsneutrons

Most elements that commonly occur are Most elements that commonly occur are made up of isotopesmade up of isotopes

For example, chlorine exists as 2 isotopes.For example, chlorine exists as 2 isotopes. A sample of chlorine gas consists of 75% A sample of chlorine gas consists of 75%

of chlorine-35 and 25% of chlorine-37of chlorine-35 and 25% of chlorine-37

Calculation: 75%(35) + 25% (37) = 35.5

Properties of IsotopesProperties of Isotopes

Isotopes Isotopes have the same chemical have the same chemical properties but slightly different properties but slightly different physical propertiesphysical properties

The The chemical properties of chemical properties of isotopes are similar as chemical isotopes are similar as chemical reactions involve only electrons.reactions involve only electrons.

The The physical properties differ physical properties differ as as the relative masses of isotopes the relative masses of isotopes differdiffer

Uses of IsotopesUses of Isotopes

Isotopes have Isotopes have emit high-energy radiation are emit high-energy radiation are called radio isotopes. A heart pacemaker called radio isotopes. A heart pacemaker is is implanted in patients with heart problems to implanted in patients with heart problems to regulate their heartbeats. Pacemakers were regulate their heartbeats. Pacemakers were powered by thepowered by the isotope plutonium-238. isotope plutonium-238.

How are electrons arranged How are electrons arranged in the atom?in the atom?

First shellClosest to nucleusAlways filled first

Can hold maximum of 2

Second shellCan hold up to 8 electrons

Third shell (Subsequent shells)Are filled next

May contain a maximum of 8or more electrons (absolute- 18)

Example: Magnesium Example: Magnesium AtomAtom

1st shell: 2 electrons

2nd shell: 8 electrons

3rd shell: 2 electrons

A magnesium atom (proton number = 12) hasA magnesium atom (proton number = 12) has 12 electrons12 electrons

Thus, itsThus, its electronic structure electronic structure oror electronic electronic configuration configuration can be represented ascan be represented as 2,8,2. 2,8,2.

Valence electronsValence electrons

Second shellCan hold up to 8 electrons

The shell that is furthest fromnucleus which contains electron

is called the outer shell or valenceshell

The electrons in this shell are called valence electrons (or

valency electrons)

A diagram of an atom’s outer electronic structure. Hence, even though sodium’s configuration is 2,8,1, we may show it this way (if instructed)

Importance of Valence Importance of Valence ElectronsElectrons

The The chemical properties of an chemical properties of an element depend on number of element depend on number of valence electronsvalence electrons

For example, For example, sodium (2,8,1)sodium (2,8,1) and and potassium (2,8,8,1)potassium (2,8,8,1) have similar have similar chemical properties as in each chemical properties as in each case there is 1 electron in the case there is 1 electron in the outer shell.outer shell.

Periodic TablePeriodic Table

In the In the periodic table, elements are periodic table, elements are arranged in order of increasing proton arranged in order of increasing proton numbernumber

The The vertical column of elements (number vertical column of elements (number of valence electron)of valence electron) called called Group Group

The The horizontal column of elements horizontal column of elements (number of electron shells)(number of electron shells) called called Period Period

Elements that have same number of Elements that have same number of valence electrons are in the same group.valence electrons are in the same group.

Hence, elements in the same group have Hence, elements in the same group have similar chemical propertiessimilar chemical properties