The Structure of the Atom History, Structure, Properties and Forces Chapter 4
Atomic Structure History, Structure and Properties of the Atom
Atomic Structure Objectives 1. I can illustrate and compare the different atomic models proposed by scientists. I can illustrate the organization of each subparticle in a neutral atom. I can distinguish between atoms of different elements and of the same elements. I can calculate the atomic mass for any element.
History of the Atom • Great Thinkers (2,000yrs. Ago) • Age of Reason and Thought • Democritus vs. Aristotle view on the make-up of matter.
Democritus(400b.c.)Greek Philosopher Observed matter to be made up of atoms. Atoms are the smallest form of matter. Atoms cannot be broken down. The types of atoms in matter determine its properties.
Aristotle: Greek Philosopher (300b.c.) Aristotle observed matter to be composed of one or more of these four elements: air, earth, fire and water. Most people believed Artistole. Why?
John Dalton’s Atomic Theory English school teacher Proved Democritus atoms hypothesis using the scientific method. His conclusions produced: Dalton’s Atomic Theory
Atoms are the building blocks of all matter. 2. Atoms cannot be subdivided. 3. Each element has the same kind of atoms. 4. In a compound, the different atoms chemically combine in the same way (fixed composition). 5. Atoms cannot be created or destroyed just rearranged. Dalton’s Atomic Theory
Thomson’s Cathode Ray Experiment J.J. Thomson (pg. 105) 1897 discovered electrons in gas atoms using a cathode ray tube. Determined electrons have a negative charge. Electrons have the same charge in all atoms.
Thomson’s Plum Pudding Model If atoms are made of electrons how come most matter does not shock us? Atoms must have positive particles, too. He proposed the Plum Pudding Atomic Model An atom is equally made up of positive and negative particles.
Goldstein’s Cathode Tube Experiment chemed.chem.purdue.edu reich-chemistry.wikispaces.com • He discovered the positively charged particle, proton, using a cathode ray tube also.
Rutherford’s Gold Foil Experiment • The laser beam consisted of positively charged alpha particles. • Hypothesized that if the Plum Pudding model of the atom was correct then the • + charged alpha particles should deflect or bend slightly when in contact with the gold foil atoms. • His experimental results revealed something different. Most alpha particles paths were not affected by any charge when in contact with gold foil. (Red straight lines on left diagram). Just a few deflected back at large angles. Knew it had to be of the same charge, because repelled.
Rutherford’s Conclusion • Most of the atom is empty space. • Small dense region composed of • (+) charged particles. • (Nucleus)
Subatomic Particle: Neutron • What keeps the protons within the nucleus ? • (Like particles repel each other) • 1932 - James Chadwick discovers the nucleus also has neutral particles present. He called them neutrons. • Neutrons have a significant mass like protons.
Bell Ringer 1. Compare the different views Aristotle and Democritus had about what matter was made of. 2. Which Greek philosopher was correct ? 3. Which later scientist proved his view?
Bell Ringer:4. a. Identify and explain this Atomic Model?b. Who concluded this atomic model?
Bell Ringer 5. Look at the following experiment below. • What was this experiment called? • Who developed this experiment? • Did his experiment prove or disprove the Plum Pudding Model?
Kandium Lab Post Lab Question • Abbreviate each isotope of Kandium using the new • symbol you assigned it and its mass number. • Using the table above convert the mass number of each • Kandium isotope from amu to grams.
Distinguishing Atoms atomic number= The number of protons within an atom’s nucleus. Atom’s I.D. Atoms of the same element always have the same number of protons. Elements are arranged numerically on the periodic table based on their atomic number.
Neutral Atoms Most matter in nature is neutral. (Doesn’t shock us!) This means the atoms making up the matter is neutral. What are the two charged subatomic particles? p+ and e- For an atom to be neutral the # of p+ = # of e-.
Atom’s Mass Mass number (amu): What contributes mass to the atom? Sum of protons and neutrons in nucleus of atom. Problem A: Selenium(Se) has an atomic # of 34 and a mass of 80 amu. How many p+, e-, and n0 are there in selenium? p+ (proton) = 34 (atomic #) e- (electron)= 34 (balance p+) n0 (neutron)= 80 – 34 = 46
Atom’s Subatomic Particles Problem B: A cesium (Cs) atom has a mass of 133 and an atomic number of 55 amu. How many p+, e-, and no are there? P+ = 55; e- = 55 ; no = 78 Problem C: An iron atom has an atomic number of 26 and 30 neutrons. • How many p+ and e- are there? P+ = 26; e- =26 • What is iron’s mass number? Mass number = 56 amu
Bell Ringer: Atomic Structure • Complete the table above. Each atom is neutral. • Rank the atoms in increasing order based on atomic number. • 3.Rank the atoms in decreasing order based on mass number. • 4.Pick one of the atoms from the table to illustrate the number of protons, electrons, and neutrons using Rutherford’s model of the atom.
An Element’s Isotopes Isotopes= atoms with different number of neutrons in their nucleus. Elements can have several isotopes. Ex. Carbon C-12 and C-14 (mass #) Mass # changes. (varied # neutrons) The number of protons and electrons stay the same.
An Element’s Isotopes C-12 C-14 # of p+, n0, e-? # of p+, n0, e-?
Element’s Isotopes • Oxygen has three isotopes. They are O-16, O-17, and O-18. • What is the mass number for each isotope of oxygen in amu? 2. What is the atomic number for each isotope of oxygen? 3. What is the number of p+, n0, and e- for each isotope of Oxygen ?
Atomic mass= the averagemassof all the element’s isotopes present within a naturally occuring sample of matter. Calculate Atomic Mass of an Element 1. Multiply the mass # of each isotope by its natural abundance ( common occurance) in decimal form. 2. Add all the isotopes products together. Atomic MassElement’s average mass
Carbon’s Atomic Mass Calculate the atomic mass for Carbon: Carbon-12 natural abundance is 98%. Carbon-14 natural abundance is 2%. Carbon’s atomic mass? 12 x 0.98 = 11.76 amu 14 x 0.02 = + 0.28 amu = 12.04 amu * Just remember to convert natural abundance from percentage to decimal form.
Mass Number vs. Atomic Mass Compare mass number of an atom with element’s atomic mass using the Venn diagram below.
Atomic Mass Calculate Iodine’s atomic mass. Watch significant figures. Answer: 126.86 = 126.9 (sig. figs)
Atomic Properties If most of the atom is empty space, why doesn’t matter pass through one another?
Atomic Properties If most of the atom is empty space, why doesn’t matter pass through one another? spiff.rit.edu
Atomic Properties What keeps the protons from leaving the nucleus and being drawn towards the electrons?
Atomic Forces • Electrostatic Forces : • Nuclear Forces:
Bell Ringer: Atomic Forces • What are the two primary forces within an atom? • Distinguish between these forces. • a. Which one of the forces is stronger ? b. Why is this important to the atom’s existence?
Atomic Forces • Electrostatic Forces : • Forces between charged particles. • Nuclear Forces: Forces that holds nucleus together
Charged Atoms Ions = charged atoms. • How do ions form? Neutral atoms lose or gain electrons. • Two types of atoms: • Cations = positively charged atoms (more p+ than e-) • Anions = negatively charged atoms (more e- than p+)