The Periodic Table and The Atomic Theory

How do patterns occur in the periodic table?

• Regular changes of the structure of the atoms of elements

• Pattern Example: Elements line up in columns because they are similar in their arrangement of electrons

What did Niels Bohr contribute?

• Suggested that electrons move around the nucleus of an atom in orbits or shells

What is a Bohr Model?

• A diagram that shows how many electrons are in each shell surrounding the nucleus of an atom

What are electron shells?

• Regions surrounding the nucleus of an atom

• Each shell is a certain distance away from the nucleus

How many electrons does each shell hold?

• 1: 2

• 2: 8

• 3:8

• 4 or greater: 32

How to draw a Bohr Diagram?

• Write the element symbol

• Check the periodic table to see how many electrons an element has

• Paying attention to how many electrons each shell can hold, figure out how many shells the atom has

• Draw a circle around the element symbol for each shell

• Use a dot to represent an electron. Start with the inner shell, put the correct number of electrons on the diagram

What does valence mean?

• Outer

What does valence electrons mean?

• Electrons in the outermost shell

What does a valence shell mean?

• highest occupied energy level

What are important trends in valence electrons and chemical families?

• Elements in same family/group have same number of valence electrons

• Elements in the same period have valence electrons in the same shell

• Period number indicated the number of shells that contain electrons

How does an atom become full and what is it called?

• Noble Gas atoms (Group 18) have filled valence shells, making them unreactive and stable

• Atoms in other groups need to gain or loose electrons to become stable (full valence shell) during a chemical reaction

What is an ion?

• Two types (positive or negative)

• Atom that gained or lost electrons, and as a result has a change

What are positive ions?

• metals

• If an atom looses electrons then the atom becomes positively charged

• Since atoms of metals have 1,2, or 3 valence electrons, they want to loose them

What are negative ions?

• Non metals

• If an atom gains electrons, then the atom is negatively charged

• Since atoms of non-metals have more than 3 valence electrons, they want to gain valence electrons

What are some trends with reactivity?

• Reactivity of an element is linked to how close it is to having a full valence shell (most reactive are groups 1 and 17)\

• Reactivity increases as you move down the group

What are some trends in atomic size?

• Increases moving down a group

• Atomic size decreases moving left to right across a period