The Atom (Basic Structure - 1) Chemistry (14 - 16) The Atom (Basic Structure - 1) © SSER Ltd.

All matter throughout the Universe is made up of atoms. The Atom All matter throughout the Universe is made up of atoms. Atoms are minute particles of matter. A speck of dust contains billions of atoms. As each individual atom is so tiny, it is impossible to see an individual atom in sufficient detail to describe its structure.

The Atom The mass of an atom is very small and is not usually expressed in grams. One gram of hydrogen atoms will contain more than 600,000 million, million, million atoms!!!

Development of the Atomic Theory Over the last two hundred years, scientific experiments have led us to a model of the atom which is widely accepted by modern scientists – this is known as the ‘Atomic Theory’.

John Dalton In 1806, the elements were defined by Dalton as being substances composed of only one type of atom. John Dalton 1766 - 1844 He also introduced the idea that atoms had a ‘solid ball’ structure. We now define an element as a substance composed of atoms, each of which has the same number of protons.

Positively charged sphere Negatively charged electron J. J. Thompson J. J. Thompson 1856 - 1940 In 1897, J. J. Thompson showed that an atom contained small negatively charged particles. He called these particles electrons. Thompson knew that the atom was neutral (had no electrical charge). Positively charged sphere He proposed that the atom must be made of a positively charged sphere which contained the negatively charged electrons. Negatively charged electron This became known as the ‘plum pudding’ model.

Earnest Rutherford E. Rutherford 1871 - 1937 In 1910, Earnest Rutherford and his research team carried out experiments in which particles were fired at a thin sheet of gold. Rutherford expected all of the particles to pass straight through...

Earnest Rutherford E. Rutherford 1871 - 1937 In 1910, Earnest Rutherford and his research team carried out experiments in which particles were fired at a thin sheet of gold. Rutherford expected all of the particles to pass straight through...

Earnest Rutherford Press ‘Start’ to take a closer look at Rutherford’s experiment... From these results, Rutherford concluded that the atom consisted of a central nucleus, which contained most of the atom’s mass, surrounded by the electrons. He also predicted the existence of neutrons in the nucleus.

The Structure of the Atom Today scientists accept that an atom contains a central nucleus around which electrons orbit in different levels. The nucleus is composed of neutrons and protons.

The Structure of the Atom Protons, neutrons, and electrons are types of sub-atomic particle. Each element has a unique combination of the three types of sub atomic particles... = Neutrons = Protons = Electrons N.B. This diagram represents a lithium atom. In reality, the electrons are very much smaller than the neutrons or protons.

The Atomic Nucleus The nucleus of an atom is tiny compared to the volume occupied by the electrons of the atom. If an atom could be enlarged to the size of a football stadium, the nucleus of the atom would be about the size of a golf ball. An electron has an incredibly small mass, which is 1/1840 the mass of a neutron or a proton. Therefore, electrons are not considered to contribute anything to the mass of an atom. Hence, the vast majority of the mass of an atom is found in the nucleus.

The Atomic Nucleus So far, the nucleus has been shown as a static body, whose sub-atomic particles fill the space of the nucleus. In fact, the nuclear particles are in constant motion.

Sub-Atomic Particles – Mass and Charge 1 Protons 1 Neutrons 1/1840 Electrons The charges on the proton and electron are opposite but equal in magnitude, so they cancel each other out exactly.

The Atom – Sub Atomic Particles For each particle drag and drop the correct answers into the table.

Does the Atom have an Electrical Charge? = 4 Neutrons = 4 x 0 charge = 0 = 3 Protons = 3 x +1 charge = +3 = 3 Electrons = 3 x -1charge = -3 Total Charge = 0 + (+3) + (-3) = 0 All atoms have an overall neutral electrical charge and therefore any atom always has an equal number of protons and electrons.

The Atom – Atomic Number and Atomic Mass To describe an atom fully, we need to know the numbers of each type of sub-atomic particle in the atom. We use these numbers to generate the atomic number and the mass number of the atom. The atomic number is the number of protons in an atom. The mass number is the sum of protons and neutrons in the atom. N.B. The electrons have an insignificant mass.

The Atom – Atomic Number and Atomic Mass An atom of Lithium (Li) can be represented as follows: Mass Number 7 Li Atomic Symbol Atomic Number 3 This shows that a Lithium (Li) atom has three protons, and four neutrons.

Li 7 Mass Number 3 Atomic Number The Lithium Atom = Neutrons 4 x = Protons 3 x = Electrons 3 x

C 12 Mass Number 6 Atomic Number The Carbon Atom = Neutrons 6 x = Protons 6 x = Electrons 6 x

The Lithium and Carbon Atoms All atoms of a particular element have the same number of protons and electrons. All lithium atoms have 3 protons and 3 electrons whereas all carbon atoms have 6 protons and 6 electrons. The Lithium Atom The Carbon Atom Therefore, the atoms of each different element have a unique number of protons and electrons.

Atomic Structure and the Periodic Table Drag the following elements, based on their atomic number, into the correct place in the periodic table.

Electron Levels (Shells) In an atom, the electrons are arranged in levels (sometimes called shells or orbitals) around the nucleus. The electrons fill the levels from the nearest level to the nucleus, outwards. Each electron level has a maximum number of electrons it can hold.

Electron Levels (Shells) The first electron level can hold up to 2 electrons. The second electron level can hold up to 8 electrons. The third electron level can hold up to 18 electrons. In this atom (Na) the first two electron levels are full but the third shell is incomplete. Note that only some nuclear particles are shown.

The Structure of Atoms Electrons do not orbit in concentric circles but have more elaborate orbits.

The Structure of Atoms If the electrons in an atom were particles ...and if we could freeze the atom at a moment in time! ...and if we had a microscope that could see the atom! ...is this what an atom would look like?

The Structure of Atoms OR ... if the electrons in an atom were particles …and in very rapid motion around the nucleus, so rapid that they appear as a blur... ...is this what an atom would look like?

Electron Levels (Shells) The first level can hold 2 electrons The electrons in different levels (shells) are represented in the following way: The first level can hold 2 electrons 2 The second level can hold 8 electrons 2,8 The third level can hold up to 18 electrons 2,8,18

The Electronic Structure for Lithium Lithium is the first element in the first short period of the Periodic Table. Its atomic number is 3, which tells us that an atom of lithium contains 3 electrons. The electron configuration for a lithium atom can be drawn like this: The electronic configuration for lithium is written as: 2, 1

The Electronic Structure for Chlorine Chlorine is in the second short period of the Periodic Table. Its atomic number is 17, which tells us that an atom of chlorine contains 17 electrons. The electrons in a chlorine atom fill the levels starting from the lower level. The electronic configuration for chlorine is written as: 2, 8, 7

Electron Levels (Shells) Drag the electrons to form the correct electronic configuration for neon (atomic number 10)…

Electron Levels (Shells) Type the correct electronic configurations of these four elements…

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