Define an ion in chemistry

Helium and hydrogen have almost the same atomic size, yet the ionization energy of helium is almost twice that of hydrogen. explain why hydrogen has a much higher ionization energy than any element in group 1 does.

A gas under an initial pressure of 0.60 atm is compressed at constant temperature from 27 L to 3.0 L. The final pressure becomes

skid marks about 6.7 km long. If the car had an initial speed of 425 km/h, estimate the coefficient of kinetic friction. The acceleration of gravity is 9.81 m/s 2.

What is the melting temperature of magnesium in kelvin

Where are the electrons located on a periodic table?

Periodic table, chemistry questions who discovered lanthanides. how did they discover it, when did they discover it.

A flask containing 155cm^3 of hydrogen was collected under a pressure of 22.5kPa. What pressure would have been required in order for the volume of the gas to have been 90.0 cm^3 at constant temperature?

Which change is most likely to occur when a molecule of H2 and a molecule of I2 collide with proper orientation and sufficient energy? 1. a chemical change, because a compound is formed 2. a chemical change, because an element is formed 3.

Which substance is a diatomic molecule? a. he b. o2 c. co2 d. h2o?

What is the difference between the electronegativity values of sodium and bromine?