How do you tell atoms apart?• All atoms have neutrons, protons and electrons.• *It is the number of protons in an atom that distinguishes one atom from another
Atomic Number• *Atomic Number – The number of protons in an element is called its atomic number. – Every element has it’s own unique atomic number.
Mass Number• *Mass Number: the total number of protons and neutrons in the nucleus of an atom is called the mass number.• Atoms of the same element have the same number of protons, but they can have different numbers of neutrons
Isotopes• *Isotopes are atoms of the same element that have different numbers of neutrons.• These are all isotopes of hydrogen:
Where are the electrons?• *Protons and neutrons are attracted to each other inside the nucleus of the atom.• *The electrons of an atom are orbiting around the nucleus in an electron cloud.
Where are the electrons?• *The electron cloud is divided into energy levels.• *The levels have less energy closer to the nucleus, more energy the further from the nucleus.• *The further an electron is from the nucleus, the more energy it has.
18.2 Comparing Atoms Key Question: What are atoms and how are they put together?*Read text section 18.2BEFORE Investigation 18.2
18.3 The Periodic Table of Elements• Elements are made up of only one kind of atom.• Compounds are made up of combinations of atoms.• Elements that are part of the same group act alike.
18.3 The Periodic Table of Elements• Dimitri Mendeleev (1834- 1907) organized information about all the known elements in a table that visually organized the similarities between them.• Mendeleev placed each element on the table in a certain row and column based on its properties.
18.3 The Periodic Table of Elements• The chemical symbol is an abbreviation of the element’s name.• The atomic number is the number of protons all atoms of that element have in their nuclei.
18.3 The Periodic Table of Elements• The mass number of an element is the total number of protons and neutrons in the nucleus.• The atomic mass is the average mass of all the known isotopes of the element.
18.3 The Periodic Table of Elements• The symbols for some elements don’t always obviously match their names.
18.3 The Periodic Table of Elements Key Question: What does atomic structure have to do with the periodic table?*Read text section 18.3 BEFORE Investigation 18.3