The Structure of the Atom Chapter 4 The Structure of the Atom

Section 1 – Early ideas about matter

The Atomic Theory Daltons Atomic Theory In 1803 John Dalton proposed a Theory to explain the laws of conservation of matter, definite proportions and multiple proportions. Theory Matter is composed of extremely small particles called atoms Atoms are indivisible and indestructible Atoms of a given element are identical in size mass and chemical properties Atoms of a specific element are different from those of another element Different atoms combine in simple whole-number ratios to form compounds In a chemical reaction atoms are separated, combined or rearranged

Section 2 – Defining the atom

The Atom Atom: The smallest unit of matter that retains the properties of that matter Imagine a Gold bar Atoms are very small and cannot be seen by the naked eye, however an instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen https://m.youtube.com/watch?v=NWWkZ2ILNmA Atom

Structure of the Atom Atoms are made up of 3 particles called sub-atomic particles Electrons Neutron Proton

Structure of the Atom Particle Symbol Location Charge Relative Mass Electron e- Space surrounding nucleus 1- 1/1840 Proton p Nucleus 1+ 1 Neutron n Atoms are spherically shaped Electrons are located outside the nucleus and are fast moving Electrons are held in the atom by its (-ve) charge being attracted to the (+ve) charge of the protons in the nucleus

Structure of the Atom Cont'd Particle Symbol Location Charge Relative Mass Electron e- Space surrounding nucleus 1- 1/1840 Proton p Nucleus 1+ 1 Neutron n Neutrons are neutral and exists in the nucleus Protons are positively charged and exist in the nucleus An atom is neutral (has no charge) this means that the # electrons = # of protons in the atom Chemical behavior can be explained by an atoms electrons

Section 3 – How atoms differ

How Atoms differ There are more than 110 different atoms that exists Atoms of different elements differ in their number of Protons

How Atoms differ Cont'd Atomic Number: The # of protons in an atom Atomic number = # protons = # electrons

How Atoms differ Cont'd

Examples Symbol Atomic # Protons Electrons Fill out the following table by determining the element, atomic number, protons and electrons given the following information: Element Name Symbol Atomic # Protons Electrons a. Lead Pb 82 b. 8 c. 30

Practice Problems (Page 116 #12, 13, 14, 15)

(You must know these for the next exam) Write out the first 20 Elements (Include their name, symbol and atomic number) (You must know these for the next exam) Hydrogen, H Helium, He Lithium, Li Beryllium, Be Boron, B Carbon, C Nitrogen, C Oxygen, O Fluorine, F Neon, Ne Sodium, Na Magnesium, Mg Aluminum, Al Silicon, Si Phosphorus, P Sulfur, S Chlorine, Cl Argon, Ar Potassium, K Calcium, Ca

Isotopes and Mass Number Elements that have the same number of protons but different numbers of neutrons These atoms keep the same chemical properties because they have the same number of electrons We use the number of neutrons or mass number to tell isotopes apart Mass number or Atomic Mass: Is the total weight of the element Mass number/ Atomic Mass = # protons + # neutrons Mass Number is always written as a decimal

Atomic Mass of Atoms Small masses expressed in scientific notation are extremely difficult to work with so scientists developed a method of measuring the mass of an atom relative to the mass of a specific atomic standard. 1 atomic mass unit (amu) = 1/12th the mass of a carbon-12 atom Carbon has an atomic mass of 12 Almost equal to one proton or one neutron

Average Atomic Mass of Elements The atomic mass of an element is the weighted average mass of the isotopes of that element

Isotopes and Average Atomic Mass (Practice Problems 16-17 page 118)

Isotopes and Average Atomic Mass (Practice Problems 18-19 page 121)

Isotopes and Average Atomic Mass (Practice Problems 18-19 page 121)

Section 4 – Unstable nuclei & radioactive decay

Radioactivity In the late 1890’s Scientists noticed some substances spontaneously emitted radiation in a process called radioactivity. This is because their nuclei is unstable Rays and particles emitted are called radiation Radioactive atoms undergo changes that alters their identity and allows them to form totally new atoms Nuclear Reaction: A reaction that involves a change in an atoms nucleus Nuclear reactions can change one element into another element

Radioactive Decay Unstable nuclei lose energy by emitting radiation is a spontaneous process called radioactive decay. Unstable atoms undergo radioactive decay until they from stable atoms which are often of a different element. https://www.youtube.com/watch?v=TJgc28csgV0

Types of Radiation Alpha Radiation Beta Radiation Gamma Radiation https://www.youtube.com/watch?v=VTHQYjkCqV0

Types of Radiation Alpha (α) Radiation The radiation that is deflected towards the negatively charged plate is called alpha radiation. An alpha particle has 2 protons and 2 neutrons and therefore has a 2+ charge (which explains why α particles are attracted to the negatively charged plates) An alpha particle is equivalent to a helium 4 nucleus and is represented by: https://www.youtube.com/watch?v=MMQ87r7fd24

Types of Radiation Alpha (α) Radiation Example: Radioactive Decay of Radioactive Radium-226 into Radon 222

Types of Radiation Beta (β) Radiation The radiation that is deflected towards the positively charged plate is called beta radiation. A beta particle article is a high speed electron with a 1- charge (which explains why β particles are attracted to the positively charged plates) An Beta particle is represented by: https://www.youtube.com/watch?v=xVS-dYazXuw

Types of Radiation Beta Radiation Example: Radioactive Decay of Carbon 14 to Nitrogen 14 Other ways to write the β particles

Types of Radiation Gamma (γ) Radiation A high energy radiation that possesses no mass and is denoted by the symbol γ. They are neutral and so are not deflected by in an electric or magnetic field. They usually accompany α & β radiation Gamm rays by themselves cannot result in the formation of a new atom. https://www.youtube.com/watch?v=5oUagoF_viQ

Types of Radiation Gamma (α) Radiation Example: Radioactive Decay of Uranium-238 into Thorium 222 or Neptunium-237