ATOMIC STRUCTURE AND THE PERIODIC TABLE

Atoms, elements and compounds

• Atoms make up everything and have a radius of around 0.1 nanometres (1 × 10^-1m)

• Neutrons have a relative mass of 1, and no charge

• Protons have a relative mass of 1, and a positive 1 charge

• Electrons have a very small mass, and a charge of negative 1

• Elements are different types of atoms, and are shown on the periodic table

  

• An isotope is an element with the same number of protons, but different numbers of neutrons, so therefore different mass numbers

• Relative atomic mass of an element’s isotopes = the sum of(isotope abundance x mass) / sum of percentage of all isotopes

  • Should be divided by 100 if all isotopes are present

• Compounds are two or more different elements that are chemically bonded

  • H₂O or CO₂, but not O₂ OR Cl₂

  • Elements in compounds are always found in the same proportions

Molecules

• Molecules are two or more atoms chemically bonded

  • For example, O₂ and CO₂ are both molecules

Electronic structure

• The first shell of an atom has 2 electrons, then 8 electrons and then 8 electrons (2,8,8)

• The group number tells you the number of electrons an element has in it’s outer shell

• The number of shells an element has is the same as the number of shells it has

The size and mass of atoms

• Atoms have a radius of around 1 × 10^-10 m, or 0.1 nanometres

• Their mass is made of the total number of neutrons and protons

Development of the model of the atom

• Democritus - Atomic theory

  • In 500 B.C

  • Everything is made up of tiny indestructible particles, with empty space between

• John Dalton - In the 1800’s

  • Everything is made up of ‘solid spheres’

  • Different types of spheres are different elements

• JJ Thompson - The plum pudding model

  • In 1897

  • He found that atoms couldn’t be solid spheres and that most contained charged particles

  • He thought the atom was a ball of positive charge with discrete negative particles embedded in it

• Ernest Rutherford - Alpha scattering experiment

  • In 1909

  • He fired positive alpha particles at a thin sheet of gold

  • If the positive mass was spread out, like in the plum pudding model, all the particles should pass through as the positive charge is not dense enough to repel

    • However, not all of the particles did and some were deflected

  • This showed that there was a concentrated positive nucleus - the nuclear model

• Niels Bohr - In 1913

  • He suggested that electrons orbit the nucleus in shells, which prevents the atom from collapsing like in Rutherford’s model (1909)

• Rutherford - In 1913

  • He suggested that the nucleus in made up of small discrete particles, called protons, and wasn’t just a cloud of charge

• James Chadwick - In 1932

  • He found that the nucleus contained neutrons with mass

The periodic table

• The periodic table was created by Dimitri Mendeleev in the mid 19th century

• He left spaces to predict new, undiscovered elements

• Columns are called group and have similar chemical properties and have the same number of electrons in the outer shell

• Rows are called periods and shows the number of shells an element has

The development of the periodic table

• Before Dimitri Mendeleev, neutron and proton scientists tried to classify their discoveries in order of atomic weights

  • They were incomplete, and the groups were often inaccurate 

• Dimitri Mendeleev made the periodic table in 1869, and he predicted new elements and left spaces in his table

  • He included elements mass number, element symbol and atomic number in his table

  • He made groups with similar chemical properties, with the same number of electrons in the outer shell

Metals and non-metals

• Metals are found on the left side of the periodic table

  • They form positive ions - they lose electrons

    • The fewer electrons they have in their outer shells, the easier they are lost

  • They get more reactive the further down the table you go

    • This is because they have more shells, so the outer shell electrons have little attraction to the nucleus and are lost easily

  • Metals metallically bond so are very strong

    • They are malleable, conductors of electricity and heat

    • They have high melting and boiling points, and they are shiny and sonorous

• Non-metals are found on the right side of the periodic table

  • They form negative ions, or none at all

  • Non-metals have lower densities than metals, are brittle and dull in colour

    • They don’t conduct and have low melting and boiling points

• The transition metals have typical metal properties

  • They can form more than one ion

    • For example, iron (II) and iron (III)

  • They also form good catalysts

Group 1 - The alkali metals

• The group 1 elements are lithium, sodium, potassium, rubidium, caesium and francium

• Their properties include:

  • Soft, low densities and low melting points, which are different to other metals

  • They get more reactive down the group

  • Their melting and boiling points decrease down the group

• They have one electron in their outer shells, which can be lost mor easily the further down the group as the are more shell

  • They are further from the nucleus, so less attraction as there is a further distance between

• They are almost always found as ionic compounds

  • With electrostatic forces between non-metal and alkali metals

• Alkali metals and water react vigorously to form metal hydroxide and hydrogen gas

• Alkali metals and chlorine gas react to form metal chloride salt

  • Na + Cl $\rightarrow$ NaCl (salt)

• Alkali metals and oxygen react to form metal oxides

  • Lithium and oxygen react to form lithium oxide

  • Sodium and oxygen react to for sodium oxide OR sodium peroxide

  • Potassium and oxygen react to form potassium peroxide OR potassium superoxide

Group 7 - The halogens

• All of the halogens are a bit dangerous ☹

• They all exist as diatomic molecules

  • Make covalent bonds to gain a full outer shell, like chlorine

• They can form covalent bonds with other non-metals as well

• Properties and trends of the halogens:

  • Their melting and boiling points increase down the group

  • Their reactivity decreases down the group as the more shells there are, the weaker forces of attraction there is from the nucleus to gain more electrons

• They form negative 1 ions with metals

  • Their name changes to end in -ide, like chloride or fluoride

• In displacement reactions, a more reactive element can displace another element that is less reactive

  • Cl₂ + 2KBr $\rightarrow$ Br₂ + 2KCl - bromide is displaced by chlorine

  • The more reactive element will always displace the less reactive one

Group 0 - The noble gases

• The noble gases exist as colourless gases

• They are all unreactive and have a full outer shell

  • They exist as singular atoms

  • They are non-flammable

  • Their boiling points increase down the group

The transition metals

• The transition metals are found in the middle of the periodic table (between groups 2 and 3)

• Their properties in comparison to group 1

  • They both conduct electricity 

  • They are both shiny 

  • They have higher melting and boiling points 

  • They have higher densities and are stronger and harder than the alkali metals

• They have slow or non-existent reactions with oxygen, water and the halogens

  • They react vigorously with group 1

• They make good catalysts

DONE!!!