The Atom-an introduction 11 DP Chemistry R Slider

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

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

The particle nature of matter Each element has a distinctive atomic number and mass number. The atomic number (Z) corresponds to the number of protons in the nucleus. The mass number (A) corresponds to the total number of neutrons and protons in the nucleus. Mathematically: A = Z + number of neutrons

Structure of the Atom The particles that make up the elements are called atoms. All atoms of one element are the same, but they are different from the atoms of all other elements. In other words, each element has a distinct type of atom with a specific number of protons, neutrons and electrons. Protons have a +ve charge Protons have a +ve charge Electrons have a –ve charge Electrons have a –ve charge Neutrons have no charge Neutrons have no charge

Structure of the Atom Protons (p) and neutrons (n) are found in the centre of the atom in the nucleus Electrons (e) are found in the surrounding space around the nucleus moving randomly in what is known as an ‘electron cloud’. Relative mass Relative charge electron(e)1/2000 proton(p)1+1 neutron(n)10

Structure of the Atom Isotopes All atoms of the same element have the same number of protons in the nucleus, however they do not necessarily have the same mass. These atoms differ in the number of neutrons and therefore, the mass number and are known as isotopes. Some well-known isotopes are in the table to the right. Name # p # n # e Hydrogen101 Deuterium111 Tritium121 Carbon Carbon Carbon Uranium Uranium

Structure of the Atom The Bohr Model Bohr’s model of the atom consists of electrons in distinct energy levels or ‘shells’. The shells closest to the nucleus are the lowest energy (n=1) and ‘fill’ first. The maximum number of electrons in each shell can be calculated by 2n 2. Therefore, n=1 maximum of 2 e n=2 maximum of 8 e n=3 maximum of 18 e and so on… The valence shell or outer shell can hold a maximum of 8.

Structure of the Atom Orbitals Schrödinger used quantum mechanics to describe the shape of the ‘clouds’ within each energy level. These are called orbitals and each energy level contains an increasing number of orbitals to accommodate more electrons. All energy levels contain ‘s’ orbitals, which are spherical (one lobe). All but the first energy level contain 3 ‘p’ orbitals, which are dumbbell shaped (two lobes). After the first two, each energy level contains 5 ‘d’ orbitals, most of which have 4 lobes. Higher energy levels contain 7 ‘f’ orbitals. Each orbital can accommodate 2 electrons. Therefore: ‘s’ orbitals hold 2 electrons ‘s’ orbitals hold 2 electrons ‘p’ orbitals hold 6 electrons ‘p’ orbitals hold 6 electrons ‘d’ orbitals hold 10 electrons ‘d’ orbitals hold 10 electrons ‘f’ orbitals hold 14 electrons ‘f’ orbitals hold 14 electrons

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

Ions – loss or gain of e- An atom that loses or gains electrons is called an ion. There are two types: 1. Cations (+): have lost electrons, making them positively charged (eg Mg 2+ loss of 2e-) 2. Anions (-): have gained electrons, making them negatively charged (eg O 2- gain of 2e-)

Ions 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 gas e- configuration as this is the most stable configuration (i.e. 8 e- in the valence shell, unless we are talking about the 1 st shell which only holds 2 e- as in He). We can predict the ions that are formed by atoms by using the Periodic Table. The group number (column number) indicates the number of e- in the valence shell. Therefore: 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. The transition metals are more difficult to predict as many of these elements have a variable e- configuration, however, these will all lose electrons to form positive ions. The transition metals are more difficult to predict as many of these elements have a variable e- configuration, however, these will all lose electrons to form positive ions. In general: Metals tend to form cations (+) and non-metals tend to form anions (-)