Elements, Atoms, and Isotopes
The Language of Chemistry CHEMICAL ELEMENTS -CHEMICAL ELEMENTS - –pure substances that cannot be decomposed by ordinary means to other substances. Sodium Bromine Aluminum
The Language of Chemistry The elements, their names, and symbols are given on the PERIODIC TABLEThe elements, their names, and symbols are given on the PERIODIC TABLE How many elements are there?How many elements are there?
The Periodic Table Dmitri Mendeleev ( )
HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS
Dalton’s Atomic Theory John Dalton ( ) proposed an atomic theory While this theory was not completely correct, it revolutionized how chemists looked at matter and brought about chemistry as we know it today instead of alchemy Thus, it’s an important landmark in the history of science.
Dalton’s Atomic Theory - Summary 1.matter is composed, indivisible particles (atoms) 2.all atoms of a particular element are identical 3.different elements have different atoms 4.atoms combine in certain whole-number ratios 5.In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.
HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON
HISTORY OF THE ATOM Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL
HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit
HISTORY OF THE ATOM gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. helium nuclei
HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.
Rutherford’s experiment.
The modern view of the atom was developed by Ernest Rutherford ( ).
Results of foil experiment if Plum Pudding model had been correct.
What Actually Happened
An atom consists of a nucleusnucleus –(of protons and neutrons) electrons in space about the nucleus.electrons in space about the nucleus. The Atom Nucleus Electron cloud
Copper atoms on silica surface. An _____ is the smallest particle of an element that has the chemical properties of the element.An _____ is the smallest particle of an element that has the chemical properties of the element. Distance across = 1.8 nanometer (1.8 x m)
ATOMIC STRUCTURE Particle proton neutron electron Charge + ve charge -ve charge No charge 1 1 nil Mass
ATOMIC COMPOSITION Protons (p + )Protons (p + ) –+ electrical charge –mass = x g –relative mass = atomic mass units (amu) but we can round to 1 Electrons (e - )Electrons (e - ) – negative electrical charge –relative mass = amu but we can round to 0 Neutrons (n o )Neutrons (n o ) – no electrical charge –mass = amu but we can round to 1
Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al Atomic number Atom symbol AVERAGE Atomic Mass
Mass Number, A C atom with 6 protons and 6 neutrons is the mass standardC atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units= 12 atomic mass units Mass Number (A) = # protons + # neutronsMass Number (A) = # protons + # neutrons NOT on the periodic table…(it is the AVERAGE atomic mass on the table)NOT on the periodic table…(it is the AVERAGE atomic mass on the table) A boron atom can have A = 5 p + 5 n = 10 amuA boron atom can have A = 5 p + 5 n = 10 amu
Isotopes Atoms of the same element (same Z) but different mass number (A).Atoms of the same element (same Z) but different mass number (A). Boron-10 ( 10 B) has 5 p and 5 nBoron-10 ( 10 B) has 5 p and 5 n Boron-11 ( 11 B) has 5 p and 6 nBoron-11 ( 11 B) has 5 p and 6 n 10 B 11 B Same number of protons… Different number of NEUTRONS!
Figure 3.10: Two isotopes of sodium.
Isotopes & Their Uses Bone scans with radioactive technetium-99.
Atomic Symbols Show the name of the element, a hyphen, and the mass number in hyphen notation sodium-23 Show the mass number and atomic number in nuclear symbol form mass number 23 Na atomic number 11
Isotopes? Which of the following represent isotopes of the same element? Which element? 234 X 234 X 235 X 238 X
Counting Protons, Neutrons, and Electrons Protons: Atomic Number (from periodic table) Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) Electrons: –If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -) –If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)
Learning Check – Counting Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C #p + _______ _______ _______ #n o _______ _______ _______ #e - _______ _______ _______
Answers 12 C 13 C 14 C #p #n o #e
Learning Check An atom has 14 protons and 20 neutrons. A.Its atomic number is 1) 142) 163) 34 B. Its mass number is 1) 142) 163) 34 C. The element is 1) Si2) Ca3) Se D.Another isotope of this element is 1) 34 X 2) 34 X 3) 36 X
One Last Learning Check Write the nuclear symbol form for the following atoms or ions: A. 8 p +, 8 n, 8 e - ___________ B.17p +, 20n, 17e - ___________ C. 47p +, 60 n, 46 e - ___________
AVERAGE ATOMIC MASS Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth.Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth. For boron atomic weightFor boron atomic weight = 0.20 (10 amu) (11 amu) = 10.8 amu = 0.20 (10 amu) (11 amu) = 10.8 amu 10 B 11 B
Isotopes & Average Atomic Mass Because of the existence of isotopes, the mass of a collection of atoms has an average value.Because of the existence of isotopes, the mass of a collection of atoms has an average value. 6 Li = 7.5% abundant and 7 Li = 92.5% 6 Li = 7.5% abundant and 7 Li = 92.5% –Avg. Atomic mass of Li = ______________ 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% 28 Si = 92.23%, 29 Si = 4.67%, 30 Si = 3.10% –Avg. Atomic mass of Si = ______________