Structure of Atoms Next > In this presentation you will: explore the structure of atoms

Next > Atoms are the smallest part of an element that can exist. It used to be thought that atoms could not be subdivided. However, we now know that atoms are made up of protons, neutrons and electrons. Introduction

Atoms are the building blocks for the whole Universe. Matter is composed of elements, which are made from small particles called atoms. Physical substances are composed of matter. Atoms are the smallest distinguishable part of an element. Each element, such as gold, is composed of just one type of atom. Next > Atoms

Atoms are not solid spheres of matter as was once thought. Although atoms are the smallest distinguishable unit of an element, they are made up of three different sub-atomic particles: Protons Electron Neutron Proton Example: carbon atom (C) Next > Neutrons Electrons Atoms

Unfortunately an atom is too small to be seen with the naked eye. It is also too small to be seen with a normal light microscope. We can draw a model to represent the atom. Next > Models Electron Neutron Proton Example: carbon atom (C)

Next > This model will have advantages and disadvantages. A good model will have more advantages than disadvantages. This does not mean that the model is perfect. Models It is a way for us to understand better how the atom is constructed. Electron Neutron Proton Example: carbon atom (C)

What is the name given to the smallest distinguishable unit of an element? A)Atom B)Molecule C)Particle D)Matter Next > Question 1

Next > What is the name given to the smallest distinguishable unit of an element? Question 1 A)Atom B)Molecule C)Particle D)Matter

Next > Example: carbon atom (C) Protons and neutrons are found in the middle of the atom, the nucleus. Electrons are much smaller than the nucleons, and orbit (move around) the nucleus at a considerable distance from it. Electron Nucleus (consisting of protons and neutrons) Atoms For this reason, protons and neutrons are often called nucleons.

Next > For example, if an atom was a soccer field, then the nucleus would be about the size of a soccer ball in the center of the field. The rest of the atom is empty space. Atoms Example: carbon atom (C) Electron Nucleus (consisting of protons and neutrons)

Which of the following is NOT found in the nucleus of any atom? A) Proton B) Neutron C) Nucleon D) Electron Next > Question 2

Next > Which of the following is NOT found in the nucleus of any atom? Question 2 A) Proton B) Neutron C) Nucleon D) Electron

Protons, neutrons and electrons have different masses and electrical charges. Both the masses and the charges are very, very small. But then these particles are also very, very small. Next > Particle Name Mass in kilograms Charge in coulombs Proton1.7 × × Neutron1.7 × Electron9.1 × × Mass and Charge If you could fill a 1 cm cube just with protons or neutrons it would have a mass of 250 million tons!

Next > Particle NameRelative Mass Relative Charge Proton1+1 Neutron10 Electron Relative Mass and Charge Nearly all the mass of an atom is in the positively charged nucleus. We take the mass of the proton as 1 and its charge as +1 then compare the masses and charges of the other particles to the proton's values Another way of comparing these quantities is to use their relative values.

Next > Relative Mass and Charge The electron mass is nearly nothing compared with that of the proton and neutron. It is electrical attraction between the positively charged nucleus and the negatively charged electrons that keeps the electrons orbiting the nucleus. Particle NameRelative Mass Relative Charge Proton1+1 Neutron10 Electron

The identity of an atom is determined by the number of protons it contains. For example, the simplest atom, hydrogen (H) always has one proton. Next > Atomic Number All atoms of the same element have the same number of protons. Example: hydrogen atom (H) One proton in the nucleus One electron

Example: carbon atom (C) 6 Electrons 6 protons in the nucleus The atomic number is equal to the number of protons in an atom's nucleus. Next > An atom of carbon (C) always has six protons. An element is determined by the atomic number of its atoms. Every element has a different atomic number. Atomic Number Example: carbon atom (C) Atomic number = 6 Example: hydrogen atom (H) Atomic number = 1

Example 2: Oxygen (O) The number of neutrons within an atom can be found by subtracting the atomic number from the mass number. The mass number of an atom is the total number of protons and neutrons in the nucleus. Example 1: Magnesium (Mg) 12 protons and 12 neutrons 8 protons and 8 neutrons Mass number = 24 Mass number = 16 Atomic number = 12 Atomic number = 8 Next > Mass Number

Atoms of the same element with different numbers of neutrons, and therefore different atomic masses, are called isotopes. Next > Atoms of an element always have the same number of protons. Isotopes Some atoms of the element may have different numbers of neutrons. Hydrogen - 1 Hydrogen - 2 Two types of hydrogen Electron Proton Neutron

Many of the most common and important elements have several naturally occurring isotopes. Carbon (C), which is found in all living things, has three isotopes: carbon-12, carbon-13 and carbon-14. Next > Isotopes Carbon-12 Mass number = 12 Atomic number = 6 Carbon-13 Mass number = 13 Atomic number = 6 Carbon-14 Mass number = 14 Atomic number = 6

Carbon-12 Mass number = 12 Atomic number = 6 Carbon-13 Mass number = 13 Atomic number = 6 Carbon-14 Mass number = 14 Atomic number = 6 Isotopes that naturally break down in this way (unstable) are called radioactive isotopes. Carbon-12 is by far the most common isotope of carbon. Next > Carbon-13 is found in smaller quantities, and carbon-14 is very rare as it easily breaks down into smaller particles. Stable Unstable (radioactive) Isotopes

Information of any element can be found on a special chart known as ‘The Periodic Table’. Each cell in the table shows an element and enables us to look up and compare the elements. 2 He Helium 4 Atomic Number Symbol Name Mass Number Typical Cell from The Periodic Table Next > The Periodic Table

The Periodic Table shows all the known elements in the universe. It also shows information such as the atomic number and mass number. Elements are arranged into rows (periods) and columns (groups). Next > The Periodic Table Periods Groups

Next > Electron Structure All chemical reactions are based around changes to the number and location of the electrons orbiting the nucleus. All atoms of elements have the same number of protons (charge +1) as electrons (charge -1), so their net charge is zero. The number and arrangement of electrons within an atom, determines the properties of an atom. Example: neon atom (Ne) ElectronProtonNeutron

''Isotopes are atoms of the same element containing the same number of protons and electrons but different numbers of neutrons.'' Is this statement true or false? Next > Question 3

True Next > ''Isotopes are atoms of the same element containing the same number of protons and electrons but different numbers of neutrons.'' Is this statement true or false? Question 3

Each electron in an atom is in a particular energy level (or shell) and the electrons must occupy the lowest available energy level. Electrons move rapidly around the nucleus (orbit) in distinct energy levels (shells). When a shell is full the next electron goes into the next lowest available energy level. Next > Example: nickel atom (Ni) Increasing energy of energy levels Energy levels (shells) Electron Structure

2 nd shell = 8 electrons Next > 1 st shell = 2 electrons Each energy level is capable of holding only a certain number of electrons. The first energy level can hold only two electrons. The second energy level can hold eight electrons. Electron Structure This energy level is filled first. This energy level is filled after the first energy level is complete (full).

Next > There are further energy levels, each containing larger numbers of electrons. The electrons in the outer shell are termed valence electrons. Electron Structure Outer shells

Electrons move rapidly around the nucleus in distinct orbits (energy levels). The second energy level can hold a maximum of… A)one electron. B)ten electrons. C)eight electrons. D)eighteen electrons. Next > Question 4

Next > Electrons move rapidly around the nucleus in distinct orbits (energy levels). The second energy level can hold a maximum of… A)one electron. B)ten electrons. C)eight electrons. D)eighteen electrons. Question 4

The reactivity of elements is the ability of a substance to react with another chemical substance to produce new products. Next > The reactivity of an element is determined entirely by its valence electron configuration. Reactivity and Valence Electrons This is because these electrons are on the outside furthest from the nucleus and nearest to other atoms.

More reactive elements have atoms containing nearly empty or nearly full outer energy levels. Next > Fluorine (F) is a very reactive element due to 7 electrons in the 2 nd outer energy level (shell). Neon (Ne) is a stable element, as it has a full outer energy level (shell). Reactivity and Valence Electrons These electron arrangements are said to be stable. Elements with atoms that have a full outer energy level are very unreactive.

This model works well. It must do, as you will find it in many textbooks and reference sources. Advantages: It allows us to visualize something that is too small to see. Next > It is not perfect. It gives us an analogy with the solar system model. It represents the energy levels (shells) as orbits. How Good is this Model?

Disadvantages: It simplifies and so distorts reality. Next > It particularly misrepresents electron behavior (but represents energy levels well). The scale is not correct. How Good is this Model?

Next > The Electron Cloud It is not possible to say where an electron is at any instant. This is an improved model. Electrons do not orbit the nucleus in circular orbits like satellites. They rotate about the nucleus in "electron clouds". We talk about the probability of where an electron is. The electron cloud represents the areas of highest probability. Nucleus Electron Clouds

In this presentation you have seen: End > how protons, neutrons and electrons are arranged in atoms how models can be used to represent concepts Summary