Atomic Theory and the Atom

Early Models of the Atom Democritus Matter could be divided until the smallest particle is reached Called these atomos Atoms could not be divided

Early Models of the Atom Dalton All elements are made of atoms that cannot be divided Atoms of the same element have the same mass Atoms cannot be changed into other atoms – may not be created or destroyed Compounds consist of atoms in a specific ratio

Early Models of the Atom Lavoisier Demonstrated that burning wood caused no change in mass Law of Conservation of Matter

Early Models of the Atom Thomson Atoms contain negatively charged particles – electrons Because atoms are neutral, he proposed a plum pudding model Negative charges scatter throughout a ball of positive charges

Early Models of the Atom Rutherford Gold foil experiments Nucleus contains particles with a positive charge - protons

Early Models of the Atom Bohr Electrons move in definite orbits around the nucleus The Atom Song

Early Models of the Atom Chadwick Noted that the mass of atoms was too large to just contain protons The neutron – no charge

Modern Model of the Atom The electron cloud Electrons may be found anywhere in a cloud-like region Movement is related to energy level

The Atomic Structure The Atom and its sub-particles Inside an Atom

Atomic Structure Proton Has a positive charge Located in the nucleus Has a mass of 1 amu Symbol p+ 

Atomic Structure Neutrons No charge Located in the nucleus Has a mass of 1 amu Symbol n 

Atomic Structure Have a negative charge Electron Have a negative charge Located in a cloud outside the nucleus Mass is 1/1836 – adds little to the atom Symbol e-

Atomic Structure Protons and neutrons found in the nucleus make up nearly all the mass of an atom An atom’s volume is the space in which the electrons move

Describing Atoms Atomic Number – the number of protons In a neutral atom, the # of protons = the # of electrons

Describing Atoms Mass Number – sum of the protons and neutrons Isotopes – atoms of the same element that have a different number of neutrons Example … C-12, C-13, C-14 Have the same properties but different masses

Isotopes The number of protons for a given atom never changes. Two atoms with different numbers of neutrons are called isotopes

Isotopes Have the same atomic number (number of protons) Have different mass numbers (number of protons + neutrons)

Isotopes

The Periodic Table Patterns in the Elements 1869 – 63 known elements Mendeleev - organizes the elements based on atomic mass - further grouping based on similar properties - able to predict the properties of three missing elements Moseley - 1913 discovered a way to measure the positive charge of an atom’s nucleus - table rearranged by atomic number; a few elements shifted

The Periodic Table Atomic Number – the number of protons Atomic Mass – the average of the masses of the isotopes based on the percentage of each found on Earth

Q: What are the three main parts of the atom, and where are they located? A: The proton and neutron are located in the nucleus. The electrons are found in the cloud surrounding the nucleus. Q: What charge do each of the particles carry? A: protons have a positive charge; electrons have a negative charge;neutrons have no charge. Q: Why do atoms have no electrical charge even though most of their particles have charges? A: The atom has an equal number of positive and negative charges.

Q: What is atomic number and how is it used to distinguish one element from another? A: Atomic number is the number of protons in each atom of a specific element. Each element has a unique atomic number; each atom of the element has the same number of protons. Q: If the atomic number of the isotope N-15 is 7, how many protons, neutrons, and electrons would it have? A: Protons = 7 Neutrons = 8 Electrons = 7

Element Atomic # Protons Neutrons Electrons Atomic Mass Al 13 27 Rb 48 85 F 9 19 K 20 Ti 22 25 Check your answers on the next slide

Element Atomic # Protons Neutrons Electrons Atomic Mass Al 13 14 27 Rb 37 48 85 F 9 10 19 K 20 39 Ti 22 25 47

Q: The information about atoms and their structure is referred to as a theory. Explain