According to the modern atomic theory, atoms are made-up of smaller subatomic particles in the nucleus. The nucleus contains two types of subatomic particles, protons and neutrons. The protons have a positively electrical charge and the neutrons have no charge. The electrons have a negative electrical charge and are able to move around the nucleus. An atom usually contains an equal number of positively charged protons and negatively charged electrons. This makes the atom itself electrically neutral. The electrons exist at different energy levels, called shells, around the nucleus where they revolve freely in a constant motion.
Carbon dioxide increases acidity when dissolved in water e.g. in blood as it reacts with the water to form carbonic acid which has a slightly acidic pH.
