And the service in these stores is also very good. Generally, the price of an eye exam in Wal-mart, Costco and Target optical can range from less than $50 (if you have an eye exam at a retail store or optical chain) to $100 or more (if you have an eye exam at a medical clinic or private eye doctor's office).
What is true about the elements of a period? (Select all that apply.) a.They have the same number of electron shells. b They have similar chemical characteristics. c They have similar physical characteristics.
This page describes the structures of the Period 3 elements from sodium to argon, and shows how these structures can be used to explain the physical properties of the elements. Variation in physical properties in period 3. Melting and boiling points. In a moment we shall explain all the ups and downs in this graph. Electrical conductivity. Sodium, magnesium and aluminium are all good conductors of electricity. Silicon is a semiconductor. None of the rest conduct electricity. Explaining the trends