The Atom-an introduction 11 DP Chemistry R Slider

The Atom-an introductionThe Atom-an introduction

11 DP Chemistry11 DP ChemistryR SliderR Slider

The particle nature of The particle nature of mattermatter

Matter is often described as being made up of small particles that Matter is often described as being made up of small particles that are continuously moving and interacting. In each of the three states are continuously moving and interacting. In each of the three states of matter (solid, liquid, gas) the particles experience vibrational of matter (solid, liquid, gas) the particles experience vibrational motion. Liquids and gases experience translational (movement) motion. Liquids and gases experience translational (movement) motion as well. Gases experience more translational motion than motion as well. Gases experience more translational motion than liquids as they have more energy.liquids as they have more energy.

liquid gassolid


The primary "particle" in chemistry is the atom. The primary "particle" in chemistry is the atom. Atoms Atoms are defined as the smallest particle of an element.are defined as the smallest particle of an element. However, you probably know that there is a However, you probably know that there is a substructure to an atom; that it is made of substructure to an atom; that it is made of protons, protons, neutrons and electronsneutrons and electrons. You may also know that . You may also know that protons and neutrons are each made of three protons and neutrons are each made of three quarksquarks. .


Each element has a Each element has a distinctive atomic distinctive atomic number and mass number and mass number.number.

The The atomic numberatomic number (Z) (Z) corresponds to the corresponds to the number of protons in number of protons in the nucleus.the nucleus.

The The mass numbermass number (A) (A) corresponds to the total corresponds to the total number of neutrons and number of neutrons and protons in the nucleus.protons in the nucleus.

Mathematically:

A = Z + number of neutrons

Structure of the AtomStructure of the Atom

The particles that make up the elements are The particles that make up the elements are called atoms. All atoms of one element are the called atoms. All atoms of one element are the same, but they are different from the atoms of same, but they are different from the atoms of all other elements. In other words, each all other elements. In other words, each element has a distinct type of atom with a element has a distinct type of atom with a specific number of protons, neutrons and specific number of protons, neutrons and electrons.electrons.

Protons have a +ve chargeProtons have a +ve charge Electrons have a –ve charge Electrons have a –ve charge Neutrons have no chargeNeutrons have no charge


Protons (p) and Protons (p) and neutrons (n)neutrons (n) are are found in the centre of found in the centre of the atom in the the atom in the nucleus nucleus

Electrons (e)Electrons (e) are are found in the found in the surrounding space surrounding space around the nucleus around the nucleus moving randomly in moving randomly in what is known as an what is known as an ‘‘electron cloudelectron cloud’.’.

RelatiRelative ve massmass

RelatiRelative ve chargchargee

electrelectronon

(e)(e)

1/2001/20000

-1-1

protonproton

(p)(p)11 +1+1

neutroneutronn

(n)(n)11 00


IsotopesIsotopesAll atoms of the same All atoms of the same

element have the same element have the same number of protons in number of protons in the nucleus, however the nucleus, however they do not necessarily they do not necessarily have the same mass. have the same mass. These atoms differ in These atoms differ in the number of neutrons the number of neutrons and therefore, the mass and therefore, the mass number and are known number and are known as isotopes. Some well-as isotopes. Some well-known isotopes are in known isotopes are in the table to the right.the table to the right.

NameName # # pp

# # nn

# # ee

Hydrogen Hydrogen 11 00 11

DeuteriuDeuteriumm

11 11 11

TritiumTritium 11 22 11

Carbon Carbon 1212

66 66 66

Carbon Carbon 1313

66 77 66

Carbon Carbon 1414

66 88 66

Uranium Uranium 235235

9292 141433

9292

Uranium Uranium 238238

9292 141466

9292

Structure of the AtomStructure of the AtomThe Bohr ModelThe Bohr ModelBohr’s model of the atom Bohr’s model of the atom

consists of electrons in consists of electrons in distinct energy levels or distinct energy levels or ‘shells’. The shells closest to ‘shells’. The shells closest to the nucleus are the lowest the nucleus are the lowest energy (n=1) and ‘fill’ first.energy (n=1) and ‘fill’ first.

The maximum number of The maximum number of electrons in each shell can be electrons in each shell can be calculated by calculated by 2n2n22..

Therefore,Therefore,n=1 maximum of 2 en=1 maximum of 2 en=2 maximum of 8 en=2 maximum of 8 en=3 maximum of 18 en=3 maximum of 18 eand so on…and so on…

The valence shell or outer shell The valence shell or outer shell can hold a maximum of 8.can hold a maximum of 8.

Structure of the AtomStructure of the AtomOrbitalsOrbitalsSchrödinger used quantum mechanics to describe the shape Schrödinger used quantum mechanics to describe the shape

of the ‘clouds’ within each energy level. These are called of the ‘clouds’ within each energy level. These are called orbitals and each energy level contains an increasing orbitals and each energy level contains an increasing number of orbitals to accommodate more electrons. All number of orbitals to accommodate more electrons. All energy levels contain ‘s’ orbitals, which are spherical (one energy levels contain ‘s’ orbitals, which are spherical (one lobe). All but the first energy level contain 3 ‘p’ orbitals, lobe). All but the first energy level contain 3 ‘p’ orbitals, which are dumbbell shaped (two lobes). After the first two, which are dumbbell shaped (two lobes). After the first two, each energy level contains 5 ‘d’ orbitals, most of which each energy level contains 5 ‘d’ orbitals, most of which have 4 lobes. Higher energy levels contain 7 ‘f’ orbitals. have 4 lobes. Higher energy levels contain 7 ‘f’ orbitals. Each orbital can accommodate 2 electrons. Therefore:Each orbital can accommodate 2 electrons. Therefore:

‘‘s’ orbitals hold 2 electronss’ orbitals hold 2 electrons ‘‘p’ orbitals hold 6 electronsp’ orbitals hold 6 electrons ‘‘d’ orbitals hold 10 electronsd’ orbitals hold 10 electrons ‘‘f’ orbitals hold 14 electronsf’ orbitals hold 14 electrons http://webfac1.enmu.edu/longro/www/orbitals/atorb.htm


Below is a representation of the relative energy Below is a representation of the relative energy levels of electron orbitals and how they appear levels of electron orbitals and how they appear around the nucleus.around the nucleus.

Ions – loss or gain of e-Ions – loss or gain of e-

An atom that loses or gains An atom that loses or gains electrons is called an ion. electrons is called an ion.

There are two typesThere are two types::

1.1. CationsCations (+): have lost electrons, (+): have lost electrons, making them positively charged (eg making them positively charged (eg MgMg2+2+ loss of 2e-) loss of 2e-)

2.2. AnionsAnions (-): have gained electrons, (-): have gained electrons, making them negatively charged (eg making them negatively charged (eg OO2- 2- gain of 2e-)gain of 2e-)

IonsIonsThe loss or gain of e- to form ions is directly related to the number of The loss or gain of e- to form ions is directly related to the number of

valence e- in an atom. All atoms have a driving force towards a noble valence e- in an atom. All atoms have a driving force towards a noble gas e- configuration as this is the most stable configuration (i.e. 8 e- gas e- configuration as this is the most stable configuration (i.e. 8 e- in the valence shell, unless we are talking about the 1in the valence shell, unless we are talking about the 1stst shell which shell which only holds 2 e- as in He).only holds 2 e- as in He).

We can predict the ions that are formed by atoms by using the Periodic We can predict the ions that are formed by atoms by using the Periodic Table. Table. The group number (column number) indicates the The group number (column number) indicates the number of e- in the valence shell.number of e- in the valence shell. Therefore: Therefore:

Group I has one valence e- and will tend to lose 1e- forming a +1 ion and Group I has one valence e- and will tend to lose 1e- forming a +1 ion and Group VII has 7 valence e- and will tend to gain 1e- forming a -1 ion, etc.Group VII has 7 valence e- and will tend to gain 1e- forming a -1 ion, etc.

The transition metals are more difficult to predict as many of these The transition metals are more difficult to predict as many of these elements have a variable e- configuration, however, these will all lose elements have a variable e- configuration, however, these will all lose electrons to form positive ions.electrons to form positive ions.

In general:In general:Metals tend to form cations (+) and non-metals tend to form Metals tend to form cations (+) and non-metals tend to form

anions (-)anions (-)

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The Atom-an introduction 11 DP Chemistry R Slider